Right in the first minutes, the Vietnamese players put pressure on their Thai rivals, and their efforts paid off in the 30th minute when Cong Phuong opened the scoring.
Trong Tuan scored the second goal with a header in the 83rd minute.
Vietnam are to meet host Indonesia, which defeated Myanmar earlier this week, in the final.
Following the match, the Vietnam Football Federation (VFF) awarded 300 million VND (12,828 USD) to coach Nguyen Quoc Tuan and his players, raising their total awards to 600 million VND.
Earlier, Vietnam beat Thailand 1-0 in its third match of the 2022 International U19 Tournament in the southern province of Binh Duong on August 9.