First of all, next time use a descriptive subject line, that makes it a lot easier to supply you with the proper help and makes it easier for people to decide if they can help you.
Second off all do a little search, searching on quota on this site yields the following usefull posts/bugs:
http://bugs.contribs.org/show_bug.cgi?id=3446http://forums.contribs.org/index.php/topic,33958.msg176151.html#msg176151I've already delete all logs in qmails but still nothing happened..Im just wondering if there's a way to the mail's database for SME server so i can delete it directly?....Thanks a lot guys. 
There is no using in deleting logfiles, the quota are counted on file ownership, logfiles are not owned by the user. You can offcourse up the limit for the affected user(s) and have them then delete e-mail and set the quota back after they have cleaned up their data/e-mail.