Hi Zhen,
[quote user="Zhen Li"]My V8i MDL created a menu item under "application".[/quote]
From V8i, a preferred method to customize MicroStation interface is to use dgnlib. Even the most of MicroStation tools in V8i use dgnlib and not any direct modifications via API. If I understand it right, it's expected if an application needs to customize GUI (menu, context menu, tools...), it will provide own dgnlib.
[quote user="Zhen Li"]How can I do it? Which example does similar function?[/quote]
Use standard customization tools: Create own dgnlib and add own icon (or group of icons or even the whole tab or workflow) where it's necessary. If you need to modify under what conditions the icon will be displayed, use Show/Hide test and Named Expressions (which can e.g. check if a variable is defined, if MDL application is loaded or many other conditions).
With regards,
Jan