两种方法：
1.
Rectangle rect = Screen.GetWorkingArea(this);
int width =
rect.Width;
int height = rect.Height;
2.
Rectangle rect = System.Windows.Forms.SystemInformation.VirtualScreen;
int width = rect.Width;
int height = rect.Height;
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原文：http://www.cnblogs.com/vincentDr/p/3576385.html