#region Win32 API

        [System.Runtime.InteropServices.DllImport("shell32.dll", EntryPoint = "ExtractAssociatedIcon")]
        private static extern IntPtr ExtractAssociatedIconA(
            IntPtr hInst,
            [System.Runtime.InteropServices.MarshalAs(
                 System.Runtime.InteropServices.UnmanagedType.LPStr)] string lpIconPath,
            ref int lpiIcon);

        [System.Runtime.InteropServices.DllImport("shell32.dll", EntryPoint = "ExtractIcon")]
        private static extern IntPtr ExtractIconA(
            IntPtr hInst,
            [System.Runtime.InteropServices.MarshalAs(
                 System.Runtime.InteropServices.UnmanagedType.LPStr)] string lpszExeFileName,
            int nIconIndex);

        private static IntPtr hInst;

        #endregion

        public static System.Drawing.Icon ExtractIcon(string fileName, int index)
        {
            if (System.IO.File.Exists(fileName) || System.IO.Directory.Exists(fileName))
            {
                System.IntPtr hIcon;

                // 文件所含图标的总数
                hIcon = ExtractIconA(hInst, fileName, -1);

                // 没取到的时候
                if (hIcon.Equals(IntPtr.Zero))
                {
                    // 取得跟文件相关的图标
                    return ExtractAssociatedIcon(fileName);
                }
                else
                {
                    // 图标的总数
                    int numOfIcons = hIcon.ToInt32();

                    if (0 <= index && index < numOfIcons)
                    {
                        hIcon = ExtractIconA(hInst, fileName, index);

                        if (!hIcon.Equals(IntPtr.Zero))
                        {
                            return System.Drawing.Icon.FromHandle(hIcon);
                        }
                        else
                        {
                            return null;
                        }
                    }
                    else
                    {
                        return null;
                    }
                }
            }
            else
            {
                return null;
            }
        }

        public static System.Drawing.Icon ExtractAssociatedIcon(string fileName)
        {
            if (System.IO.File.Exists(fileName) || System.IO.Directory.Exists(fileName))
            {
                int i = 0;

                IntPtr hIcon = ExtractAssociatedIconA(hInst, fileName, ref i);

                if (!hIcon.Equals(IntPtr.Zero))
                {
                    return System.Drawing.Icon.FromHandle(hIcon);
                }
                else
                {
                    return null;
                }
            }
            else
            {
                return null;
            }
        }

●取得代码
        string exeFullName = "F:\\test\\SetIcon\\enDataBaseSetting.exe";
        System.Drawing.Icon icon = ExtractIcon(exeFullName, 0);
        appIcon = icon.ToBitmap();
●根据实际路径取得图标
        System.Drawing.Image appIcon= System.Drawing.Bitmap.FromFile("F:\\test\\SetIcon\\images2\\App.ico");
●取得资源中的图标（此图标必须在资源【Resource】中存在）
        System.IO.Stream stream = System.Reflection.Assembly.GetExecutingAssembly().GetManifestResourceStream(PROGRAM_ICON);
            System.Drawing.Image appIcon = new System.Drawing.Bitmap(stream);
●将取得的图标赋给一个按钮
        button1.Image = appIcon.GetThumbnailImage(32, 32, null, IntPtr.Zero);