It was China's second gold of the day, following Feng Zhe's title on parallel bars.
Aly Raisman, who missed a medal in the all-around because she was on the short end of the tiebreak rules, was initially fourth. But she questioned her score and judges revised it, giving her an additional .10 in difficulty. That gave her a 15.066, identical to Romania's Catalina Ponor. But Raisman got the bronze because of a higher execution mark.
Gabby Douglas was seventh after a fall. But she finishes the London Olympics with gold medals, including the all-around title, gymnastics' biggest prize.