diff --git a/mindinsight/backend/explainer/explainer_api.py b/mindinsight/backend/explainer/explainer_api.py
index 34c74d3a..1d14a396 100644
--- a/mindinsight/backend/explainer/explainer_api.py
+++ b/mindinsight/backend/explainer/explainer_api.py
@@ -40,8 +40,52 @@ URL_PREFIX = settings.URL_PATH_PREFIX + settings.API_PREFIX
 BLUEPRINT = Blueprint("explainer", __name__, url_prefix=URL_PREFIX)
 
 
+def _validate_type(param, name, expected_types):
+    """
+    Common function to validate type.
+
+    Args:
+        param (object): Parameter to be validated.
+        name (str): Name of the parameter.
+        expected_types (type, tuple[type]): Expected type(s) of param.
+
+    Raises:
+        ParamTypeError: When param is not an instance of expected_types.
+    """
+
+    if not isinstance(param, expected_types):
+        raise ParamTypeError(name, expected_types)
+
+
+def _validate_value(param, name, expected_values):
+    """
+    Common function to validate values of param.
+
+    Args:
+        param (object): Parameter to be validated.
+        name (str): Name of the parameter.
+        expected_values (tuple) : Expected values of param.
+
+    Raises:
+        ParamValueError: When param is not in expected_values.
+    """
+
+    if param not in expected_values:
+        raise ParamValueError(f"Valid options for {name} are {expected_values}, but got {param}.")
+
+
 def _image_url_formatter(train_id, image_path, image_type):
-    """Returns image url."""
+    """
+    Returns image url.
+
+    Args:
+        train_id (str): Id that specifies explain job.
+        image_path (str): Local path or unique string that specifies the image for query.
+        image_type (str): Image query type.
+
+    Returns:
+        str, url string for image query.
+    """
     data = {
         "train_id": train_id,
         "path": image_path,
@@ -69,38 +113,48 @@ def _read_post_request(post_request):
 
 
 def _get_query_sample_parameters(data):
-    """Get parameter for query."""
+    """
+    Get parameter for query.
+
+    Args:
+        data (dict): Dict that contains request info.
+
+    Returns:
+        dict, key-value pairs to call backend query functions.
+
+    Raises:
+        ParamMissError: If train_id info is not in the request.
+        ParamTypeError: If certain key is not in the expected type in the request.
+        ParamValueError: If certain key does not have the expected value in the request.
+    """
 
     train_id = data.get("train_id")
     if train_id is None:
         raise ParamMissError('train_id')
 
     labels = data.get("labels")
-    if labels is not None and not isinstance(labels, list):
-        raise ParamTypeError("labels", (list, None))
+    if labels is not None:
+        _validate_type(labels, "labels", list)
     if labels:
         for item in labels:
-            if not isinstance(item, str):
-                raise ParamTypeError("element of labels", str)
+            _validate_type(item, "element of labels", str)
 
     limit = data.get("limit", 10)
     limit = Validation.check_limit(limit, min_value=1, max_value=100)
     offset = data.get("offset", 0)
     offset = Validation.check_offset(offset=offset)
     sorted_name = data.get("sorted_name", "")
+    _validate_value(sorted_name, "sorted_name", ('', 'confidence', 'uncertainty'))
+
     sorted_type = data.get("sorted_type", "descending")
-    if sorted_name not in ("", "confidence", "uncertainty"):
-        raise ParamValueError(f"sorted_name: {sorted_name}, valid options: '' 'confidence' 'uncertainty'")
-    if sorted_type not in ("ascending", "descending"):
-        raise ParamValueError(f"sorted_type: {sorted_type}, valid options: 'confidence' 'uncertainty'")
+    _validate_value(sorted_type, "sorted_type", ("ascending", "descending"))
 
     prediction_types = data.get("prediction_types")
-    if prediction_types is not None and not isinstance(prediction_types, list):
-        raise ParamTypeError("prediction_types", (list, None))
+    if prediction_types is not None:
+        _validate_type(prediction_types, "element of labels", list)
     if prediction_types:
         for item in prediction_types:
-            if item not in ['TP', 'FN', 'FP']:
-                raise ParamValueError(f"Item of prediction_types must be in ['TP', 'FN', 'FP'], but got {item}.")
+            _validate_value(item, "element of prediction_types", ('TP', 'FN', 'FP'))
 
     query_kwarg = {"train_id": train_id,
                    "labels": labels,
@@ -114,7 +168,17 @@ def _get_query_sample_parameters(data):
 
 @BLUEPRINT.route("/explainer/explain-jobs", methods=["GET"])
 def query_explain_jobs():
-    """Query explain jobs."""
+    """
+    Query explain jobs.
+
+    Returns:
+        Response, contains dict that stores base directory, total number of jobs and their detailed job metadata.
+
+    Raises:
+        ParamMissError: If train_id info is not in the request.
+        ParamTypeError: If one of (offset, limit) is not integer in the request.
+        ParamValueError: If one of (offset, limit) does not have the expected value in the request.
+    """
     offset = request.args.get("offset", default=0)
     limit = request.args.get("limit", default=10)
     offset = Validation.check_offset(offset=offset)
@@ -132,7 +196,15 @@ def query_explain_jobs():
 
 @BLUEPRINT.route("/explainer/explain-job", methods=["GET"])
 def query_explain_job():
-    """Query explain job meta-data."""
+    """
+    Query explain job meta-data.
+
+    Returns:
+        Response, contains dict that stores metadata of the requested job.
+
+    Raises:
+        ParamMissError: If train_id info is not in the request.
+    """
     train_id = get_train_id(request)
     if train_id is None:
         raise ParamMissError("train_id")
@@ -143,7 +215,16 @@ def query_explain_job():
 
 @BLUEPRINT.route("/explainer/saliency", methods=["POST"])
 def query_saliency():
-    """Query saliency map related results."""
+    """
+    Query saliency map related results.
+
+    Returns:
+        Response, contains dict that stores number of samples and the detailed sample info.
+
+    Raises:
+        ParamTypeError: If certain key is not in the expected type in the request.
+        ParamValueError: If certain key does not have the expected value in the request.
+    """
     data = _read_post_request(request)
     query_kwarg = _get_query_sample_parameters(data)
     explainers = data.get("explainers")
@@ -169,7 +250,16 @@ def query_saliency():
 
 @BLUEPRINT.route("/explainer/hoc", methods=["POST"])
 def query_hoc():
-    """Query hierarchical occlusion related results."""
+    """
+    Query hierarchical occlusion related results.
+
+    Returns:
+        Response, contains dict that stores number of samples and the detailed sample info.
+
+    Raises:
+        ParamTypeError: If certain key is not in the expected type in the request.
+        ParamValueError: If certain key does not have the expected value in the request.
+    """
     data = _read_post_request(request)
 
     query_kwargs = _get_query_sample_parameters(data)
@@ -193,7 +283,15 @@ def query_hoc():
 
 @BLUEPRINT.route("/explainer/evaluation", methods=["GET"])
 def query_evaluation():
-    """Query saliency explainer evaluation scores."""
+    """
+    Query saliency explainer evaluation scores.
+
+    Returns:
+        Response, contains dict that stores evaluation scores.
+
+    Raises:
+        ParamMissError: If train_id info is not in the request.
+    """
     train_id = get_train_id(request)
     if train_id is None:
         raise ParamMissError("train_id")
@@ -206,7 +304,12 @@ def query_evaluation():
 
 @BLUEPRINT.route("/explainer/image", methods=["GET"])
 def query_image():
-    """Query image."""
+    """
+    Query image.
+
+    Returns:
+        bytes, image binary content for UI to demonstrate.
+    """
     train_id = get_train_id(request)
     if train_id is None:
         raise ParamMissError("train_id")
@@ -230,6 +333,6 @@ def init_module(app):
     Init module entry.
 
     Args:
-        app: the application obj.
+        app (flask.app): The application obj.
     """
     app.register_blueprint(BLUEPRINT)
diff --git a/mindinsight/datavisual/data_transform/summary_watcher.py b/mindinsight/datavisual/data_transform/summary_watcher.py
index a9322840..c55be672 100644
--- a/mindinsight/datavisual/data_transform/summary_watcher.py
+++ b/mindinsight/datavisual/data_transform/summary_watcher.py
@@ -220,10 +220,7 @@ class SummaryWatcher:
                 summary_dict[relative_path].update(job_dict)
 
             if summary_dict[relative_path]['create_time'] < ctime:
-                summary_dict[relative_path].update({
-                    'create_time': ctime,
-                    'update_time': mtime,
-                })
+                summary_dict[relative_path].update({'create_time': ctime, 'update_time': mtime})
                 job_dict = _get_explain_job_info(summary_base_dir, relative_path, timestamp)
                 summary_dict[relative_path].update(job_dict)
 
@@ -243,12 +240,10 @@ class SummaryWatcher:
             if not is_find:
                 return
 
-            profiler = {
-                'directory': os.path.join('.', entry.name),
-                'create_time': ctime,
-                'update_time': mtime,
-                "profiler_type": profiler_type
-            }
+            profiler = {'directory': os.path.join('.', entry.name),
+                        'create_time': ctime,
+                        'update_time': mtime,
+                        "profiler_type": profiler_type}
 
             if relative_path in summary_dict:
                 summary_dict[relative_path]['profiler'] = profiler
diff --git a/mindinsight/explainer/common/enums.py b/mindinsight/explainer/common/enums.py
index d2c29f5e..d5a473c3 100644
--- a/mindinsight/explainer/common/enums.py
+++ b/mindinsight/explainer/common/enums.py
@@ -1,4 +1,4 @@
-# Copyright 2020 Huawei Technologies Co., Ltd
+# Copyright 2020-2021 Huawei Technologies Co., Ltd
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -50,3 +50,16 @@ class CacheStatus(enum.Enum):
     NOT_IN_CACHE = "NOT_IN_CACHE"
     CACHING = "CACHING"
     CACHED = "CACHED"
+
+
+class ExplanationKeys(enum.Enum):
+    """Query type enums."""
+    HOC = "hoc_layers"  # HOC: Hierarchical Occlusion, an explanation method we propose
+    SALIENCY = "saliency_maps"
+
+
+class ImageQueryTypes(enum.Enum):
+    """Image query type enums."""
+    ORIGINAL = 'original'  # Query for the original image
+    OUTCOME = 'outcome'  # Query for outcome of HOC explanation
+    OVERLAY = 'overlay'  # Query for saliency maps overlay
diff --git a/mindinsight/explainer/encapsulator/_hoc_pil_apply.py b/mindinsight/explainer/encapsulator/_hoc_pil_apply.py
index 2e0f8996..00113a6e 100644
--- a/mindinsight/explainer/encapsulator/_hoc_pil_apply.py
+++ b/mindinsight/explainer/encapsulator/_hoc_pil_apply.py
@@ -63,7 +63,7 @@ def pil_apply_edit_steps(image, mask, edit_steps, by_masking=False, inplace=Fals
     Args:
         image (PIL.Image): The input image in RGB mode.
         mask (Union[str, int, tuple[int, int, int], PIL.Image.Image]): The mask to apply on the image, could be string
-            e.g. 'gaussian:9', a single, grey scale intensity [0, 255], a RBG tuple or a PIL Image object.
+            e.g. 'gaussian:9', a single, grey scale intensity [0, 255], an RBG tuple or a PIL Image object.
         edit_steps (list[EditStep]): Edit steps to be drawn.
         by_masking (bool): Whether to use masking method. Default: False.
         inplace (bool): True to draw on the input image, otherwise draw on a cloned image.
@@ -99,7 +99,7 @@ def _pil_apply_edit_steps_unmask(image, mask, edit_steps, inplace=False):
     Args:
         image (PIL.Image): The input image.
         mask (Union[int, tuple[int, int, int], PIL.Image]): The mask to apply on the image, could be a single grey
-            scale intensity [0, 255], a RBG tuple or a PIL Image.
+            scale intensity [0, 255], an RBG tuple or a PIL Image.
         edit_steps (list[EditStep]): Edit steps to be drawn.
         inplace (bool): True to draw on the input image, otherwise draw on a cloned image.
 
@@ -132,7 +132,7 @@ def _pil_apply_edit_steps_mask(image, mask, edit_steps, inplace=False):
     Args:
         image (PIL.Image): The input image.
         mask (Union[int, tuple[int, int, int], PIL.Image]): The mask to apply on the image, could be a single grey
-            scale intensity [0, 255], a RBG tuple or a PIL Image.
+            scale intensity [0, 255], an RBG tuple or a PIL Image.
         edit_steps (list[EditStep]): Edit steps to be drawn.
         inplace (bool): True to draw on the input image, otherwise draw on a cloned image.
 
diff --git a/mindinsight/explainer/encapsulator/datafile_encap.py b/mindinsight/explainer/encapsulator/datafile_encap.py
index 249b6858..5c1eaf8d 100644
--- a/mindinsight/explainer/encapsulator/datafile_encap.py
+++ b/mindinsight/explainer/encapsulator/datafile_encap.py
@@ -21,6 +21,7 @@ import numpy as np
 from PIL import Image
 
 from mindinsight.datavisual.common.exceptions import ImageNotExistError
+from mindinsight.explainer.common.enums import ImageQueryTypes
 from mindinsight.explainer.encapsulator._hoc_pil_apply import EditStep, pil_apply_edit_steps
 from mindinsight.explainer.encapsulator.explain_data_encap import ExplainDataEncap
 from mindinsight.utils.exceptions import FileSystemPermissionError
@@ -63,41 +64,10 @@ class DatafileEncap(ExplainDataEncap):
             image_type (str): Image type, Options: 'original', 'overlay' or 'outcome'.
 
         Returns:
-            bytes, image binary.
+            bytes, image binary content for UI to demonstrate.
         """
-        if image_type == "outcome":
-            sample_id, label, layer = image_path.strip(".jpg").split("_")
-            layer = int(layer)
-            job = self.job_manager.get_job(train_id)
-            samples = job.samples
-            label_idx = job.labels.index(label)
-
-            chosen_sample = samples[int(sample_id)]
-            original_path_image = chosen_sample['image']
-            abs_image_path = os.path.join(self.job_manager.summary_base_dir, _clean_train_id_b4_join(train_id),
-                                          original_path_image)
-            if self._is_forbidden(abs_image_path):
-                raise FileSystemPermissionError("Forbidden.")
-            try:
-                image = Image.open(abs_image_path)
-            except FileNotFoundError:
-                raise ImageNotExistError(f"train_id:{train_id} path:{image_path} type:{image_type}")
-            except PermissionError:
-                raise FileSystemPermissionError(f"train_id:{train_id} path:{image_path} type:{image_type}")
-            except OSError:
-                raise UnknownError(f"Invalid image file: train_id:{train_id} path:{image_path} type:{image_type}")
-
-            edit_steps = []
-            boxes = chosen_sample["hierarchical_occlusion"][label_idx]["hoc_layers"][layer]["boxes"]
-            mask = chosen_sample["hierarchical_occlusion"][label_idx]["mask"]
-
-            for box in boxes:
-                edit_steps.append(EditStep(layer, *box))
-            image_cp = pil_apply_edit_steps(image, mask, edit_steps)
-            buffer = io.BytesIO()
-            image_cp.save(buffer, format=_PNG_FORMAT)
-
-            return buffer.getvalue()
+        if image_type == ImageQueryTypes.OUTCOME.value:
+            return self._get_hoc_image(image_path, train_id)
 
         abs_image_path = os.path.join(self.job_manager.summary_base_dir,
                                       _clean_train_id_b4_join(train_id),
@@ -108,7 +78,7 @@ class DatafileEncap(ExplainDataEncap):
 
         try:
 
-            if image_type != "overlay":
+            if image_type != ImageQueryTypes.OVERLAY.value:
                 # no need to convert
                 with open(abs_image_path, "rb") as fp:
                     return fp.read()
@@ -153,3 +123,41 @@ class DatafileEncap(ExplainDataEncap):
         base_dir = os.path.realpath(self.job_manager.summary_base_dir)
         path = os.path.realpath(path)
         return not path.startswith(base_dir)
+
+    def _get_hoc_image(self, image_path, train_id):
+        """Get hoc image for image data demonstration in UI."""
+
+        sample_id, label, layer = image_path.strip(".jpg").split("_")
+        layer = int(layer)
+        job = self.job_manager.get_job(train_id)
+        samples = job.samples
+        label_idx = job.labels.index(label)
+
+        chosen_sample = samples[int(sample_id)]
+        original_path_image = chosen_sample['image']
+        abs_image_path = os.path.join(self.job_manager.summary_base_dir, _clean_train_id_b4_join(train_id),
+                                      original_path_image)
+        if self._is_forbidden(abs_image_path):
+            raise FileSystemPermissionError("Forbidden.")
+
+        image_type = ImageQueryTypes.OUTCOME.value
+        try:
+            image = Image.open(abs_image_path)
+        except FileNotFoundError:
+            raise ImageNotExistError(f"train_id:{train_id} path:{image_path} type:{image_type}")
+        except PermissionError:
+            raise FileSystemPermissionError(f"train_id:{train_id} path:{image_path} type:{image_type}")
+        except OSError:
+            raise UnknownError(f"Invalid image file: train_id:{train_id} path:{image_path} type:{image_type}")
+
+        edit_steps = []
+        boxes = chosen_sample["hierarchical_occlusion"][label_idx]["hoc_layers"][layer]["boxes"]
+        mask = chosen_sample["hierarchical_occlusion"][label_idx]["mask"]
+
+        for box in boxes:
+            edit_steps.append(EditStep(layer, *box))
+        image_cp = pil_apply_edit_steps(image, mask, edit_steps)
+        buffer = io.BytesIO()
+        image_cp.save(buffer, format=_PNG_FORMAT)
+
+        return buffer.getvalue()
diff --git a/mindinsight/explainer/encapsulator/explain_data_encap.py b/mindinsight/explainer/encapsulator/explain_data_encap.py
index 4dee8f86..c2110be5 100644
--- a/mindinsight/explainer/encapsulator/explain_data_encap.py
+++ b/mindinsight/explainer/encapsulator/explain_data_encap.py
@@ -15,13 +15,13 @@
 """Common explain data encapsulator base class."""
 
 import copy
-from enum import Enum
 
+from mindinsight.explainer.common.enums import ExplanationKeys
 from mindinsight.utils.exceptions import ParamValueError
 
 
 def _sort_key_min_confidence(sample, labels):
-    """Samples sort key by the min. confidence."""
+    """Samples sort key by the minimum confidence."""
     min_confidence = float("+inf")
     for inference in sample["inferences"]:
         if labels and inference["label"] not in labels:
@@ -32,7 +32,7 @@ def _sort_key_min_confidence(sample, labels):
 
 
 def _sort_key_max_confidence(sample, labels):
-    """Samples sort key by the max. confidence."""
+    """Samples sort key by the maximum confidence."""
     max_confidence = float("-inf")
     for inference in sample["inferences"]:
         if labels and inference["label"] not in labels:
@@ -43,7 +43,7 @@ def _sort_key_max_confidence(sample, labels):
 
 
 def _sort_key_min_confidence_sd(sample, labels):
-    """Samples sort key by the min. confidence_sd."""
+    """Samples sort key by the minimum confidence_sd."""
     min_confidence_sd = float("+inf")
     for inference in sample["inferences"]:
         if labels and inference["label"] not in labels:
@@ -55,7 +55,7 @@ def _sort_key_min_confidence_sd(sample, labels):
 
 
 def _sort_key_max_confidence_sd(sample, labels):
-    """Samples sort key by the max. confidence_sd."""
+    """Samples sort key by the maximum confidence_sd."""
     max_confidence_sd = float("-inf")
     for inference in sample["inferences"]:
         if labels and inference["label"] not in labels:
@@ -65,11 +65,6 @@ def _sort_key_max_confidence_sd(sample, labels):
             max_confidence_sd = confidence_sd
     return max_confidence_sd
 
-class ExplanationKeys(Enum):
-    """Query type enums."""
-    HOC = "hoc_layers"  # HOC: Hierarchical Occlusion, an explanation method we propose
-    SALIENCY = "saliency_maps"
-
 
 class ExplainDataEncap:
     """Explain data encapsulator base class."""
@@ -105,9 +100,9 @@ class ExplanationEncap(ExplainDataEncap):
             sorted_name (str): Field to be sorted.
             sorted_type (str): Sorting order, 'ascending' or 'descending'.
             prediction_types (list[str]): Prediction type filter.
-            drop_type (str, None): When it is None, no filer will be applied. When it is 'hoc_layers', samples without
-                hoc explanations will be filtered out. When it is 'saliency_maps', samples without saliency explanations
-                will be filtered out.
+            drop_type (str, None): When it is None, all data will be kept. When it is 'hoc_layers', samples without
+                hoc explanations will be drop out. When it is 'saliency_maps', samples without saliency explanations
+                will be drop out.
 
         Returns:
              list[dict], samples to be queried.
diff --git a/mindinsight/explainer/encapsulator/explain_job_encap.py b/mindinsight/explainer/encapsulator/explain_job_encap.py
index 1c9e5ddd..da2d1df2 100644
--- a/mindinsight/explainer/encapsulator/explain_job_encap.py
+++ b/mindinsight/explainer/encapsulator/explain_job_encap.py
@@ -29,11 +29,13 @@ class ExplainJobEncap(ExplainDataEncap):
     def query_explain_jobs(self, offset, limit):
         """
         Query explain job list.
+
         Args:
             offset (int): Page offset.
-            limit (int): Max. no. of items to be returned.
+            limit (int): Maximum number of items to be returned.
+
         Returns:
-            tuple[int, list[Dict]], total no. of jobs and job list.
+            tuple[int, list[Dict]], total number of jobs and job list.
         """
         total, dir_infos = self.job_manager.get_job_list(offset=offset, limit=limit)
         job_infos = [self._dir_2_info(dir_info) for dir_info in dir_infos]
diff --git a/mindinsight/explainer/encapsulator/hierarchical_occlusion_encap.py b/mindinsight/explainer/encapsulator/hierarchical_occlusion_encap.py
index 42e3eae6..0b0bf440 100644
--- a/mindinsight/explainer/encapsulator/hierarchical_occlusion_encap.py
+++ b/mindinsight/explainer/encapsulator/hierarchical_occlusion_encap.py
@@ -15,7 +15,8 @@
 """Hierarchical Occlusion encapsulator."""
 
 from mindinsight.datavisual.common.exceptions import TrainJobNotExistError
-from mindinsight.explainer.encapsulator.explain_data_encap import ExplanationEncap, ExplanationKeys
+from mindinsight.explainer.common.enums import ExplanationKeys, ImageQueryTypes
+from mindinsight.explainer.encapsulator.explain_data_encap import ExplanationEncap
 
 
 class HierarchicalOcclusionEncap(ExplanationEncap):
@@ -81,7 +82,10 @@ class HierarchicalOcclusionEncap(ExplanationEncap):
         Returns:
             dict, the edited sample info.
         """
-        sample["image"] = self._get_image_url(job.train_id, sample["image"], "original")
+        original = ImageQueryTypes.ORIGINAL.value
+        outcome = ImageQueryTypes.OUTCOME.value
+
+        sample["image"] = self._get_image_url(job.train_id, sample["image"], original)
         inferences = sample["inferences"]
         i = 0  # init index for while loop
         while i < len(inferences):
@@ -91,9 +95,9 @@ class HierarchicalOcclusionEncap(ExplanationEncap):
                 continue
             new_list = []
             for idx, hoc_layer in enumerate(inference_item[ExplanationKeys.HOC.value]):
-                hoc_layer["outcome"] = self._get_image_url(job.train_id,
-                                                           f"{sample['id']}_{inference_item['label']}_{idx}.jpg",
-                                                           "outcome")
+                hoc_layer[outcome] = self._get_image_url(job.train_id,
+                                                         f"{sample['id']}_{inference_item['label']}_{idx}.jpg",
+                                                         outcome)
                 new_list.append(hoc_layer)
             inference_item[ExplanationKeys.HOC.value] = new_list
             i += 1
diff --git a/mindinsight/explainer/encapsulator/saliency_encap.py b/mindinsight/explainer/encapsulator/saliency_encap.py
index 4634b264..789694f0 100644
--- a/mindinsight/explainer/encapsulator/saliency_encap.py
+++ b/mindinsight/explainer/encapsulator/saliency_encap.py
@@ -15,7 +15,8 @@
 """Saliency map encapsulator."""
 
 from mindinsight.datavisual.common.exceptions import TrainJobNotExistError
-from mindinsight.explainer.encapsulator.explain_data_encap import ExplanationEncap, ExplanationKeys
+from mindinsight.explainer.common.enums import ExplanationKeys, ImageQueryTypes
+from mindinsight.explainer.encapsulator.explain_data_encap import ExplanationEncap
 
 
 class SaliencyEncap(ExplanationEncap):
@@ -32,6 +33,7 @@ class SaliencyEncap(ExplanationEncap):
                             prediction_types=None):
         """
         Query saliency maps.
+
         Args:
             train_id (str): Job ID.
             labels (list[str]): Label filter.
@@ -65,7 +67,8 @@ class SaliencyEncap(ExplanationEncap):
 
     def _touch_sample(self, sample, job, explainers):
         """
-        Final editing the sample info.
+        Final edit on single sample info.
+
         Args:
             sample (dict): Sample info.
             job (ExplainJob): Explain job.
@@ -74,14 +77,17 @@ class SaliencyEncap(ExplanationEncap):
         Returns:
             dict, the edited sample info.
         """
+        original = ImageQueryTypes.ORIGINAL.value
+        overlay = ImageQueryTypes.OVERLAY.value
+
         sample_cp = sample.copy()
-        sample_cp["image"] = self._get_image_url(job.train_id, sample['image'], "original")
+        sample_cp["image"] = self._get_image_url(job.train_id, sample['image'], original)
         for inference in sample_cp["inferences"]:
             new_list = []
             for saliency_map in inference[ExplanationKeys.SALIENCY.value]:
                 if explainers and saliency_map["explainer"] not in explainers:
                     continue
-                saliency_map["overlay"] = self._get_image_url(job.train_id, saliency_map['overlay'], "overlay")
+                saliency_map[overlay] = self._get_image_url(job.train_id, saliency_map[overlay], overlay)
                 new_list.append(saliency_map)
             inference[ExplanationKeys.SALIENCY.value] = new_list
         return sample_cp
diff --git a/mindinsight/explainer/manager/explain_loader.py b/mindinsight/explainer/manager/explain_loader.py
index 302eda65..db4f4a94 100644
--- a/mindinsight/explainer/manager/explain_loader.py
+++ b/mindinsight/explainer/manager/explain_loader.py
@@ -270,7 +270,7 @@ class ExplainLoader:
         Update the update_time manually.
 
         Args:
-            new_time stamp (datetime.datetime or float): Updated time for the summary file.
+            new_time (datetime.datetime or float): Updated time for the summary file.
         """
         if isinstance(new_time, datetime):
             self._loader_info['update_time'] = new_time.timestamp()
@@ -333,11 +333,10 @@ class ExplainLoader:
 
     def get_all_samples(self) -> List[Dict]:
         """
-        Return a list of sample information cached in the explain job
+        Return a list of sample information cached in the explain job.
 
         Returns:
-            sample_list (List[SampleObj]): a list of sample objects, each object
-                consists of:
+            sample_list (list[SampleObj]): a list of sample objects, each object consists of:
 
                 - id (int): Sample id.
                 - name (str): Basename of image.
@@ -406,7 +405,7 @@ class ExplainLoader:
                 }
 
         Args:
-            benchmarks (benchmark_container): Parsed benchmarks data from summary file.
+            benchmarks (BenchmarkContainer): Parsed benchmarks data from summary file.
         """
         explainer_score = self._benchmark['explainer_score']
         label_score = self._benchmark['label_score']
@@ -429,7 +428,7 @@ class ExplainLoader:
         Parse the sample event.
 
         Detailed data of each sample are store in self._samples, identified by sample_id. Each sample data are stored
-        in the following structure.
+        in the following structure:
 
             - ground_truth_labels (list[int]): A list of ground truth labels of the sample.
             - ground_truth_probs (list[float]): A list of confidences of ground-truth label from black-box model.
diff --git a/mindinsight/explainer/manager/explain_manager.py b/mindinsight/explainer/manager/explain_manager.py
index 7d650698..17710c95 100644
--- a/mindinsight/explainer/manager/explain_manager.py
+++ b/mindinsight/explainer/manager/explain_manager.py
@@ -65,7 +65,7 @@ class ExplainManager:
 
         Args:
             reload_interval (int): Specify the loading period in seconds. If interval == 0, data will only be loaded
-            once. Default: 0.
+                once. Default: 0.
         """
         thread = threading.Thread(target=self._repeat_loading,
                                   name='explainer.start_load_thread',
@@ -80,10 +80,10 @@ class ExplainManager:
         If explain job w.r.t given loader_id is not found, None will be returned.
 
         Args:
-            loader_id (str): The id of expected ExplainLoader
+            loader_id (str): The id of expected ExplainLoader.
 
-        Return:
-            explain_job
+        Returns:
+            ExplainLoader, the data loader specified by loader_id.
         """
         self._check_status_valid()
 
@@ -111,17 +111,19 @@ class ExplainManager:
         Return List of explain jobs. includes job ID, create and update time.
 
         Args:
-            offset (int): An offset for page. Ex, offset is 0, mean current page is 1. Default value is 0.
-            limit (int): The max data items for per page. Default value is 10.
+            offset (int): An offset for page. Ex, offset is 0, mean current page is 1. Default: 0.
+            limit (int): The max data items for per page. Default: 10.
 
         Returns:
-            tuple[total, directories], total indicates the overall number of explain directories and directories
-                    indicate list of summary directory info including the following attributes.
+            tuple, the elements of the returned tuple are:
+
+                - total (int): The overall number of explain directories
+                - dir_infos (list): List of summary directory info including the following attributes:
 
-                - relative_path (str): Relative path of summary directory, referring to settings.SUMMARY_BASE_DIR,
-                                        starting with "./".
-                - create_time (datetime): Creation time of summary file.
-                - update_time (datetime): Modification time of summary file.
+                    - relative_path (str): Relative path of summary directory, referring to settings.SUMMARY_BASE_DIR,
+                         starting with "./".
+                    - create_time (datetime): Creation time of summary file.
+                    - update_time (datetime): Modification time of summary file.
         """
         total, dir_infos = \
             self._summary_watcher.list_explain_directories(self._summary_base_dir, offset=offset, limit=limit)
@@ -216,7 +218,7 @@ class ExplainManager:
         return loader
 
     def _add_loader(self, loader):
-        """add loader to the loader_pool."""
+        """Add loader to the loader_pool."""
         if loader.train_id not in self._loader_pool:
             self._loader_pool[loader.train_id] = loader
         else:
diff --git a/mindinsight/explainer/manager/explain_parser.py b/mindinsight/explainer/manager/explain_parser.py
index ec6aaebd..70177008 100644
--- a/mindinsight/explainer/manager/explain_parser.py
+++ b/mindinsight/explainer/manager/explain_parser.py
@@ -1,4 +1,4 @@
-# Copyright 2020 Huawei Technologies Co., Ltd
+# Copyright 2020-2021 Huawei Technologies Co., Ltd
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -59,12 +59,13 @@ class ExplainParser(_SummaryParser):
 
         Args:
             filenames (list[str]): File name list.
+
         Returns:
-            tuple, will return (file_changed, is_end, event_data),
+            tuple, the elements of the tuple are:
 
-                file_changed (bool): True if the 9latest file is changed.
-                is_end (bool): True if all the summary files are finished loading.
-                event_data (dict): return an event data, key is field.
+                - file_changed (bool): True if the latest file is changed.
+                - is_end (bool): True if all the summary files are finished loading.
+                - event_data (dict): Event data where keys are explanation field.
         """
         summary_files = self.sort_files(filenames)
 
@@ -134,6 +135,12 @@ class ExplainParser(_SummaryParser):
 
         Args:
             event_str (str): Message event string in summary proto, data read from file handler.
+
+        Returns:
+            tuple, the elements of the result tuple are:
+
+                - field_list (list): Explain fields to be parsed.
+                - tensor_value_list (list): Parsed data with respect to the field list.
         """
 
         logger.debug("Start to parse event string. Event string len: %s.", len(event_str))
@@ -172,10 +179,13 @@ class ExplainParser(_SummaryParser):
     @staticmethod
     def _add_image_data(tensor_event_value):
         """
-        Parse image data based on sample_id in Explain message
+        Parse image data based on sample_id in Explain message.
 
         Args:
-            tensor_event_value: the object of Explain message
+            tensor_event_value (Event): The object of Explain message.
+
+        Returns:
+            SampleContainer, a named tuple containing sample data.
         """
         inference = InferfenceContainer(
             ground_truth_prob=tensor_event_value.inference.ground_truth_prob,
@@ -205,10 +215,10 @@ class ExplainParser(_SummaryParser):
         Parse benchmark data from Explain message.
 
         Args:
-            tensor_event_value: the object of Explain message
+            tensor_event_value (Event): The object of Explain message.
 
         Returns:
-            benchmark_data: An object containing benchmark.
+            BenchmarkContainer, a named tuple containing benchmark data.
         """
         benchmark_data = BenchmarkContainer(
             benchmark=tensor_event_value.benchmark,
@@ -223,10 +233,10 @@ class ExplainParser(_SummaryParser):
         Parse  metadata from Explain message.
 
         Args:
-            tensor_event_value: the object of Explain message
+            tensor_event_value (Event): The object of Explain message.
 
         Returns:
-            benchmark_data: An object containing metadata.
+            MetadataContainer, a named tuple containing benchmark data.
         """
         metadata_value = MetadataContainer(
             metadata=tensor_event_value.metadata,