According to the L.A. Times

At least three minutes of Sony's sci-fi comedy have been excised for its Chinese theatrical run.

Edited parts include:

• A Chinese-restaurant shootout between evil aliens and Will Smith's Agent J and Tommy Lee Jones' Agent K, the aliens are disguised as restaurant workers
• A moment when Smith’s J  “neuralyzes,” or memory-wipes, a group of Chinese bystanders

Newspaper the China Southern Daily, speculated that the latter scene may have been cut because it could be viewed as a comment on China's censorship of the Internet.

Check out some of the edited scenes here: