The second leg of the semifinal ended goalless despite many efforts from Vietnam.
Being led two goals from the first leg, Vietnam played pressing from the beginning of the game and created many dangerous chances.
One attack in the 28th minute forced goalkeeper Chatchai Budprom to come outside the box for clearance. After this attempt, he had to leave the field on a stretcher.
Vietnam had 14 shots, including four shots on goal, compared to Thailand's six shots and one shot on goal.
But that was not enough for the defending champions to make a difference.
Five-time winners Thailand will face Indonesia in the final on December 29 and January 1.