diff --git a/shadowsocks-csharp/Controller/System/SystemProxy.cs b/shadowsocks-csharp/Controller/System/SystemProxy.cs
index 63e2a8b0..ccf18ff1 100644
--- a/shadowsocks-csharp/Controller/System/SystemProxy.cs
+++ b/shadowsocks-csharp/Controller/System/SystemProxy.cs
@@ -27,7 +27,7 @@ namespace Shadowsocks.Controller
                 {
                     if (global)
                     {
-                        Sysproxy.SetIEProxy(true, true, "127.0.0.1:" + config.localPort.ToString(), "");
+                        Sysproxy.SetIEProxy(true, true, "127.0.0.1:" + config.localPort.ToString(), null);
                     }
                     else
                     {
@@ -40,12 +40,12 @@ namespace Shadowsocks.Controller
                         {
                             pacUrl = pacSrv.PacUrl;
                         }
-                        Sysproxy.SetIEProxy(true, false, "", pacUrl);
+                        Sysproxy.SetIEProxy(true, false, null, pacUrl);
                     }
                 }
                 else
                 {
-                    Sysproxy.SetIEProxy(false, false, "", "");
+                    Sysproxy.SetIEProxy(false, false, null, null);
                 }
             }
             catch (ProxyException ex)
diff --git a/shadowsocks-csharp/Util/SystemProxy/Sysproxy.cs b/shadowsocks-csharp/Util/SystemProxy/Sysproxy.cs
index ce28bdeb..f4e31f5e 100644
--- a/shadowsocks-csharp/Util/SystemProxy/Sysproxy.cs
+++ b/shadowsocks-csharp/Util/SystemProxy/Sysproxy.cs
@@ -1,83 +1,130 @@
-using System;
-using System.Collections.Generic;
-using System.Diagnostics;
-using System.IO;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
-using Shadowsocks.Controller;
-using Shadowsocks.Properties;
-
-namespace Shadowsocks.Util.SystemProxy
-{
-    public static class Sysproxy
-    {
-
-        enum RET_ERRORS : int
-        {
-            RET_NO_ERROR = 0,
-            INVALID_FORMAT = 1,
-            NO_PERMISSION = 2,
-            SYSCALL_FAILED = 3,
-            NO_MEMORY = 4,
-            INVAILD_OPTION_COUNT = 5,
-        };
-
-        static Sysproxy()
-        {
-            try
-            {
-                FileManager.UncompressFile(Utils.GetTempPath("sysproxy.exe"),
-                    Environment.Is64BitOperatingSystem ? Resources.sysproxy64_exe : Resources.sysproxy_exe);
-            }
-            catch (IOException e)
-            {
-                Logging.LogUsefulException(e);
-            }
-        }
-
-        public static void SetIEProxy(bool enable, bool global, string proxyServer, string pacURL)
-        {
-            string arguments;
-
-            if (enable)
-            {
-                if (global)
-                {
-                    arguments = $"global {proxyServer} <local>;localhost;127.*;10.*;172.16.*;172.17.*;172.18.*;172.19.*;172.20.*;172.21.*;172.22.*;172.23.*;172.24.*;172.25.*;172.26.*;172.27.*;172.28.*;172.29.*;172.30.*;172.31.*;172.32.*;192.168.*";
-                }
-                else
-                {
-                    arguments = $"pac {pacURL}";
-                }
-            }
-            else
-            {
-                arguments = "off";
-            }
-
-            using (var process = new Process())
-            {
-                // Configure the process using the StartInfo properties.
-                process.StartInfo.FileName = Utils.GetTempPath("sysproxy.exe");
-                process.StartInfo.Arguments = arguments;
-                process.StartInfo.WorkingDirectory = Utils.GetTempPath();
-                process.StartInfo.WindowStyle = ProcessWindowStyle.Hidden;
-                process.StartInfo.UseShellExecute = false;
-                process.StartInfo.RedirectStandardError = true;
-                process.StartInfo.CreateNoWindow = true;
-                process.Start();
-
-                var error = process.StandardError.ReadToEnd();
-
-                process.WaitForExit();
-
-                var exitCode = process.ExitCode;
-                if (exitCode != (int) RET_ERRORS.RET_NO_ERROR)
-                {
-                    throw new ProxyException(error);
-                }
-            }
-        }
-    }
-}
+using System;
+using System.Diagnostics;
+using System.IO;
+using System.Text;
+using Shadowsocks.Controller;
+using Shadowsocks.Properties;
+
+namespace Shadowsocks.Util.SystemProxy
+{
+    public static class Sysproxy
+    {
+        private static bool _userSettingsRecorded = false;
+
+        // In general, this won't change
+        // format:
+        //  <flags><CR-LF>
+        //  <proxy-server><CR-LF>
+        //  <bypass-list><CR-LF>
+        //  <pac-url>
+        private static string[] _userSettings = new string[4];
+
+        enum RET_ERRORS : int
+        {
+            RET_NO_ERROR = 0,
+            INVALID_FORMAT = 1,
+            NO_PERMISSION = 2,
+            SYSCALL_FAILED = 3,
+            NO_MEMORY = 4,
+            INVAILD_OPTION_COUNT = 5,
+        };
+
+        static Sysproxy()
+        {
+            try
+            {
+                FileManager.UncompressFile(Utils.GetTempPath("sysproxy.exe"),
+                    Environment.Is64BitOperatingSystem ? Resources.sysproxy64_exe : Resources.sysproxy_exe);
+            }
+            catch (IOException e)
+            {
+                Logging.LogUsefulException(e);
+            }
+        }
+
+        public static void SetIEProxy(bool enable, bool global, string proxyServer, string pacURL)
+        {
+            string str;
+            if (_userSettingsRecorded == false)
+            {
+                // record user settings
+                ExecSysproxy("query", out str);
+                ParseQueryStr(str);
+                _userSettingsRecorded = true;
+            }
+            string arguments;
+
+            if (enable)
+            {
+                arguments = global
+                    ? $"global {proxyServer} <local>;localhost;127.*;10.*;172.16.*;172.17.*;172.18.*;172.19.*;172.20.*;172.21.*;172.22.*;172.23.*;172.24.*;172.25.*;172.26.*;172.27.*;172.28.*;172.29.*;172.30.*;172.31.*;172.32.*;192.168.*"
+                    : $"pac {pacURL}";
+            }
+            else
+            {
+                // restore user settings
+                var flags = _userSettings[0];
+                var proxy_server = _userSettings[1] ?? "-";
+                var bypass_list = _userSettings[2] ?? "-";
+                var pac_url = _userSettings[3] ?? "-";
+                arguments = $"set {flags} {proxy_server} {bypass_list} {pac_url}";
+
+                // have to get new settings
+                _userSettingsRecorded = false;
+            }
+
+            ExecSysproxy(arguments, out str);
+        }
+
+        private static void ExecSysproxy(string arguments, out string queryStr)
+        {
+            using (var process = new Process())
+            {
+                // Configure the process using the StartInfo properties.
+                process.StartInfo.FileName = Utils.GetTempPath("sysproxy.exe");
+                process.StartInfo.Arguments = arguments;
+                process.StartInfo.WorkingDirectory = Utils.GetTempPath();
+                process.StartInfo.WindowStyle = ProcessWindowStyle.Hidden;
+                process.StartInfo.UseShellExecute = false;
+                process.StartInfo.RedirectStandardError = true;
+                process.StartInfo.RedirectStandardOutput = true;
+
+                // Need to provide encoding info, or output/error strings we got will be wrong.
+                process.StartInfo.StandardOutputEncoding = Encoding.Unicode;
+                process.StartInfo.StandardErrorEncoding = Encoding.Unicode;
+
+                process.StartInfo.CreateNoWindow = true;
+                process.Start();
+
+                var stderr = process.StandardError.ReadToEnd();
+                var stdout = process.StandardOutput.ReadToEnd();
+
+                process.WaitForExit();
+
+                var exitCode = process.ExitCode;
+                if (exitCode != (int)RET_ERRORS.RET_NO_ERROR)
+                {
+                    throw new ProxyException(stderr);
+                }
+
+                if (arguments == "query" && stdout.IsNullOrWhiteSpace())
+                {
+                    // we cannot get user settings
+                    throw new ProxyException("failed to query wininet settings");
+                }
+                queryStr = stdout;
+            }
+        }
+
+        private static void ParseQueryStr(string str)
+        {
+            _userSettings = str.Split(new string[] { "\r\n" }, StringSplitOptions.RemoveEmptyEntries);
+            for (var i = 0; i < 4; i++)
+            {
+                // handle output from WinINET
+                if (_userSettings[i] == "(null)")
+                    _userSettings[i] = null;
+            }
+        }
+    }
+}
\ No newline at end of file