WPF有一个
Separator控件，只是为了这个目的，它也会分离你的菜单项，当出现在工具栏上。从MSDN文档：
A Separator control draws a line,
horizontal or vertical,between items
in controls,such as ListBox,Menu,
and ToolBar. Separator controls do not
react to any keyboard,mouse,mouse
wheel,or tablet input and cannot be
enabled or selected.
在代码中：
using System.Windows.Controls; // Menu myMenu = new Menu(); myMenu.Items.Add(new Separator());