I want to restore a deleted folder.

Hi Cai. 

Welcome to the Box Community, I'm happy to help!

Box stores files and folders you place in the trash for a certain period of time. That default period is 30 days, although Box administrators of business and enterprise accounts can shorten or lengthen it.  For your type of account that is a Personal Lite account, it's 30 days. Beyond this period, files or folders purged from your Box trash may not be recoverable and may be lost forever. 

To learn more about managing Box Trash, please take a look at this article: https://support.box.com/hc/en-us/articles/360044196093-Managing-Trash

All the best,