She earned the medal in the women's one-meter springboard category at the My Dinh Water Sports Stadium in Hanoi.
Mai, 24, competed against seven others from Vietnam, Thailand, Singapore, Malaysia and the Philippines and got 224 points.
Two Malaysian athletes, Nur Dhabitah Sabri and Kimberly Bong Qian Ping, won the gold and silver with 290.45 points and 230 points, respectively.
Mai had also won a bronze at the previous edition of the games.
Later on Sunday afternoon, Nguyen Tung Duong and Phuong The Anh won the silver medal in the men's three-meter synchro category.
The gold medal was won by Malaysian duo Chew Yi Wei and Ooi Tze Liang.
The 31st SEA Games, a biennial regional multi-sport event, is being held in Hanoi and several northern provinces this month.