MyBB Community Forums

there is no problem in subforum
I create new subforums from acp


but they are not shown in my forum

Probably the fault of the theme you are using.

but before few days everything go fine
but now when i add subforum it is not shown

You could also try manually rebuilding your caches in Admin CP -> Tools.

Also make sure forum visibility of the forums in question is checked.

Do you still have the default theme installed in your board, it wouldn't hurt to try if the forums show in the default theme.