Tran Bao Toan's goal from a header at the end of the first half secured Vietnam the final victory, and their second against Thailand in the tournament.
They also beat Thailand 1-0 in the group stage.
In the third edition of the tournament, held in Cambodia, Vietnam had four matches where they scored nine goals and conceded none.
The results are even more remarkable given the fact that 23 out of 27 registered for the tournament were infected with Covid and the team needed to constantly add players from Vietnam, with many having little practice time.
The team entered the final with better preparation as some players have recovered from Covid.
Thailand entered the game more smoothly and made dangerous finishes. But they failed to score any goals.
Vietnam only started to launch effective passes near the end of the first half, and one of them was successful.
They kept the momentum with beautiful shots in the second half, although none were accurate enough to change the scoreboard.