Hi Nhan Rao,
Currently, there is no main animation property which is respected by all sub-menus. Instead, you need to set the animation settings to each sub-menu individually. If you, for example, have a sub-menu opened from RadMenuItem1, consider using the following code snippet:
.radMenuItem1.DropDown.FadeAnimationType = Telerik.WinControls.UI.FadeAnimationType.None;
I hope this helps. If you have additional questions, feel free to contact me.
the Telerik team