Vien helped her Army team win the championship with a total of 16 gold, five silver and two bronze medals at the five-day championship at Danang's Aquatic Sport Centre.
However, fourteen-year-old Nguyen Diep Phuong Tram from HCM City's National Sport Centre 2 beat Vien to win the women's 50m freestyle gold at the National Swimming Championships.
Tram also set a new record on the final day.
Tram clocked 26.37 seconds, 35 hundredth of a second faster than Vien, and broke the previous record (26.70sec) set by Vien last year.
It was the second time that Tram, a rising teen star, had beaten Vien in the championship.
HCM City team ranked second in the medal tally, bagging 14 golds, six silvers and six bronzes.
Hoang Quy Phuoc bagged five golds to help Danang to third place with just those five gold medals.
Vien, 19, finished first in the women's 200m butterfly with a time of 2 minutes and 13.79 seconds, five seconds faster than Tram in the race.
Vien then beat Tram again in the women's 400m individual medley with a time in 4min 48.73sec, while Tram took a time of 5min 1.63sec.
The Army swimmer completed her ‘golden day' with a gold medal in the 200m freestyle.
She swam in 2min 2.7sec, five hundredth of a second faster than Tram (2min 7.1sec).
HCM City's Tran Duy Khoi bagged eight golds and one silver medal, half of the total gold medals for HCM City team at the championship.