The Chinese swimmer had broken Grant Hackett's long-standing world mark at last year's World Championships in Shanghai.
The 20-year-old led from start to finish as he touched in at 14:31.02, taking more than three seconds off his own mark and prompting an emotional celebration.
Canada's Ryan Cochrane was second ahead of defending champion Oussama Mellouli.
Earlier, Ranomi Kromowidjojo claimed the sprint double by winning gold in the women's 50m Freestyle.
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