The man jumped from the platform this evening at Xuanwumen station on the Subway Line 2, officials of the Beijing Mass Transit Railway Operation Corporation Limited said.
He was killed in the incident, state-run Xinhua news agency reported.
Armed policemen and subway staff evacuated passengers from a train and medical staff later arrived.
The station was forced to close and trains running clockwise on the line had to be halted.
The service resumed later, the report said.
The incident occurred as the ruling Communist Party of China (CPC) held its Plenum to finalise a host of new economic reforms amid concerns over growing divide between rich and poor.