The 22-year-old triumphed for the first time since her Paris Games exploits with a ruthless 21-12, 21-8 victory over the unseeded Gao in the southern city of Shenzhen.
It was An's fourth win on the BWF World Tour this year and cemented her status as the undoubted top player in women's badminton.
"I'm happy beyond words to win this title. I was determined to succeed," said An.
In the men's final, Denmark's third seed Anders Antonsen was an equally emphatic 21-15, 21-13 winner over sixth-seeded Indonesian Jonatan Christie.
The top players will now gear up for the season-ending BWF World Tour Finals on December 11-15 in Hangzhou, China.
