The 23-year-old Dong swapped places with fellow countryman and eventual bronze medallist Chunlong Lu, who took gold in Beijing four years ago and is only five days older than Dong.
Dong has been keeping a journal of his London Olympic experiences and after he won gold, he admitted Friday's entry would be very simple.
"I thought about that yesterday and I think I will write 'ha ha'," the 23-year-old said.
Dong had won bronze in Beijing and his exuberant 10-move final routine won over not only the judges but the crowd, who erupted in cheers when he left the trampoline exhausted with his arms around his coach.
Lu said he became a bit emotional during the podium ceremony with the thought that a nagging injury could rule him out of further Olympics.
"I was just getting a little bit emotional because this could be the last Olympics I'm in because of the injury," he said.