Zhang Shangwu performed gymnastic stunts at a metro station in Beijing, showed pictures on a microblogging site, the Shanghai Daily reported.
At age 18, Zhand won two gold medals at the 2001 Summer Universiade in Beijing.
Zhang was training for the 2004 Athens Olympics when he sustained an injury that forced his retirement in 2003.
Langfeng, who had made the post on the microblogging site, said Zhang had to give up his professional career when he ruptured a tendon in his heel.
He tweeted that Zhang performed some of the moves which used to earn him gold medals.