||Thanks for your reply.
But it is too sensitive and always recalculate (that wastes time if using an algorithm for obtaining those graphics) and redraws the graphics using axMapControl1_OnBeforeScreenDraw, even though the extent of MapControl has no change (not only depending on ESRI ToolbarControl, but also other events, like window is hidden and shown).
However, axMapControl1_OnExtentUpdated is applied only based on the extent change (mainly from ESRI ToolbarControl). If the window of MapControl is hidden and shown by other, the graphics won't be recalculated and redraw, instead of displaying the graphics by MapControl.
But the problem is that I couldn't get correct current extent from axMapControl1_OnExtentUpdated.