The scores were 19-25, 25-19, 25-22, 21-25 and 16-14.
It was another big win for the host country which defeated Japan, the tournament's second seed after China, earlier in the tournament.
In Saturday's final at 6pm, Thailand, ranked 16th in the world, will meet Japan, which prevailed over South Korea late Friday. Japan won the championship the last time it was held in Nakhon Ratchasima, in 2007.
The Thais have won the Asian title only once before, in 2009 when they defeated the Chinese, who are 12-time Asian champions. In 2011, Thailand finished fourth in the tournament.
The Chatchai Hall, the 5,000-seat venue where Thailand and China competed, was surrounded by floodwater on Friday due to heavy rain.
However, people had started queueing to buy tickets for the match at 4am and there were some disturbances.
Stadium officers had to regulate the queues by allowing one person to buy a single ticket only, causing dissatisfaction among family members who wanted to take their children to the event.