Feng scored 15.966 to take gold ahead of Germany's Marcel Nguyen in silver medal position with a total of 15.800, while France's Hamilton Sabot took bronze.
It was the first Olympic Games medal for France on the Parallel Bars, Sabot managing to hang on after he was the second to compete and scored 15.566.
Afterwards, Deng could hardly hide his delight. He said: 'My goal after 2008 was to have a breakthrough in an individual event. Now I have.
'We were almost perfect at these Olympics. It's good for us for the future.'