Li set the record in three minutes and 51.30 seconds, breaking the old world record of 3:53.92 set by Australia's double Olympic champion Titmus at the 2018 world championships in Hangzhou, China.
"I was surprised with my result. I have returned to the pool only for two months since I took a vacation after the FINA World Championships in Budapest, Hungary," Xinhua news agency quoted Li as saying.
"I hope I could get faster and do my best in the upcoming Melbourne worlds," she said, referring to the Dec. 13-18 world championships.
The swimmer was part of China's gold-winning 4x200m freestyle relay team and bagged bronze in the 400m freestyle at the Tokyo Games last year.
She is also the reigning short course world champion in 400m and 800m freestyle events.
