1. 设置窗体无边框

设计器属性中设置：

或者代码中设置：

this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.None;

2. WinAPI帮助类

public class WinAPI
{
	public const int WM_NCLBUTTONDOWN = 0xA1;
	public const int HT_CAPTION = 0x2;
	public const int MOUSEWHEEL = 0x020A;

	[DllImportAttribute("user32.dll")]
	internal static extern int SendMessage(IntPtr hWnd, int Msg, int wParam, int lParam);

	[DllImportAttribute("user32.dll")]
	internal static extern int SendMessage(IntPtr hWnd, int Msg, IntPtr wParam, IntPtr lParam);

	[DllImportAttribute("user32.dll")]
	internal static extern bool ReleaseCapture();

}

3. 窗体上使用

设计器属性中设置鼠标移动事件

 或者代码中

// 给窗体增加鼠标移动事件
this.MouseMove += new System.Windows.Forms.MouseEventHandler(this.FrmLogin_MouseMove);
// 鼠标移动事件内，调用WinAPI实现拖拽功能
private void FrmLogin_MouseMove(object sender, MouseEventArgs e)
{
	if (e.Button == MouseButtons.Left)
	{
		WinAPI.ReleaseCapture();
		WinAPI.SendMessage(Handle, WinAPI.WM_NCLBUTTONDOWN, WinAPI.HT_CAPTION, 0);
	}
}