when i enabled "Allow comments on "Page" pages, too?" in the theme setting.
then goto my wordpress control panel-->settings-->discussion, and enabled " Break comments into pages with comments per page and the lastfirst page displayed by default
I found that the last break comment page displayed all the comments(should be the number which i config in the wordpress, e.g=20), also include all the comments in the previous break comment page.
The previous comment page was ok(only display 20 comments)
I belive this was the theme issue, because when i try to change to another theme, the break comment page works fine.