According to Liang Jianwei, vice head of the Beijing municipal traffic administration corps, costumes and masks are likely to attract the attention of other passengers.
When a lot of people stop to watch, the risk of stampedes increases, he said.
He also suggested that passengers avoid forming flash mobs in the underground.
"Although such behavior is not banned by law, passengers should not be too willful," said Liang.
Police will warn against problematic behavior when they come across it, he said.
Law enforcement teams began patrolling Beijing subway stations and trains on May 1.
During the past fortnight, they have encountered 83 cases of improper behavior, including hawking, begging and distributing advertising flyers, state-run Xinhua news agency reported.
