public partial class Form1 : Form
    {
        Timer timer = new Timer();
        public Form1()
        {
            InitializeComponent();
            timer.Interval = 100;
            timer.Start();

            timer.Tick += delegate
            {
                string s = "";
                switch (Control.MouseButtons)
                {
                    case MouseButtons.Left: s = "Left"; break;
                    case MouseButtons.Middle: s = "Middle"; break;
                    case MouseButtons.Right: s = "Right"; break;
                }
                this.Text = s;
            };
        }
    }

------解决方案--------------------
  if (MouseButtons == MouseButtons.Left)
               MessageBox.Show("mouse left click ");