const int HWND_BROADCAST = 0xffff;
        const int WM_SETTINGCHANGE = 0x001A;
        public enum SendMessageTimeoutFlags : uint
        {
            SMTO_NORMAL = 0x0000,
            SMTO_BLOCK = 0x0001,
            SMTO_ABORTIFHUNG = 0x0002,
            SMTO_NOTIMEOUTIFNOTHUNG = 0x0008
        }
        [DllImport("user32.dll", SetLastError = true, CharSet = CharSet.Auto)]
        public static extern IntPtr SendMessageTimeout(IntPtr hWnd, uint Msg, IntPtr wParam, string lParam,
             SendMessageTimeoutFlags flags, uint timeout, out IntPtr result);
        static void SetUserPath(string path)   //设置用户环境变量
        {
            RegistryKey registryKey = Registry.CurrentUser.OpenSubKey(@"Environment", true);
            Console.WriteLine("Path: {0}  {1}", registryKey.GetValue("Path"), registryKey.GetValueKind("Path"));
            registryKey.SetValue("Path", registryKey.GetValue("Path") + path, RegistryValueKind.ExpandString);
            SendMessageTimeout(new IntPtr(HWND_BROADCAST), WM_SETTINGCHANGE, IntPtr.Zero, "Environment",
                SendMessageTimeoutFlags.SMTO_ABORTIFHUNG, 5000, out IntPtr result);
            Console.WriteLine("result: {0}", result);
        }

        static void SetSystemPath(string path)    //设置系统环境变量
        {
            String subKeyPath = @"SYSTEM\CurrentControlSet\Control\Session Manager\Environment";
            RegistryKey registryKey = Registry.LocalMachine.OpenSubKey(subKeyPath, true);   //需要管理员权限运行
            Console.WriteLine("Path: {0}  {1}", registryKey.GetValue("Path"), registryKey.GetValueKind("Path"));
            registryKey.SetValue("Path", registryKey.GetValue("Path") + path, RegistryValueKind.ExpandString);
            SendMessageTimeout(new IntPtr(HWND_BROADCAST), WM_SETTINGCHANGE, IntPtr.Zero, "Environment",
                SendMessageTimeoutFlags.SMTO_ABORTIFHUNG, 5000, out IntPtr result);
            Console.WriteLine("result: {0}", result);
        }
        //手动修改环境变量时，系统自动维护其类型，长度较短时为REG_SZ(String)，达到一定长度后为REG_EXPAND_SZ(ExpandString)
        //REG_SZ型注册表值项的名称是长度固定的文本字符串，最大长度不能超过255个字符；REG_EXPAND_SZ是长度可变的数据字符串。

        SetUserPath(@"C:\tcc");
        SetSystemPath(@"C:\tcc"); //需要管理员权限