Both legs will be played at the Khorfakkan Futsal Club Hall in the United Arab Emirates with the first scheduled for today (May 20) and the second on Tuesday.
Today’s game kicks off at 4pm, Thai time.
In the other play-off, Vietnam face Lebanon on Sunday and May 25 at the same venue.
The winners of the two play-offs will complete the list of Asian representatives at the World Cup in Lithuania in September.
Japan, Iran and Uzbekistan have already earned berths in the finals thanks to their results in the recent AFC Futsal Championship.
Thailand striker Muhammad Ousmanmusa said Iraq have a couple of players from their U23 team who beat Thailand a few years ago.
“We want to take revenge against Iraq,” he said.
“We will do our best and want to qualify for the World Cup again.”
Thailand have previously played in five finals.
To beat Iraq, Thailand must be sharper up front, according to their coach Jose Maria Mendes, who is better known as Pulpis.
The Thais beat the UAE 1-0 in a warm-up match at the weekend and Pulpis said they have to improve their finishing.
“We had 26 shots but could only score one goal,” said the Spanish coach.
Thailand manager said the team would receive about B3 million in bonus from sponsors if they qualify for the World Cup finals.
The World Cup Lithuania 2021 will get underway on Sept 12, with the final to be held in the city of Klaipeda on Oct 3.