First round: 12 teams played home-and-away over two legs. The six winners advanced to the second round.
Second round: 40 teams were divided into eight groups of five teams to play home-and-away round-robin matches. The eight group winners and the four best group runners-up advanced to the third round of FIFA World Cup qualification as well as qualifying for the 2019 AFC Asian Cup finals.
Third round: The 12 teams which had advanced from the second round were divided into two groups of six teams to play home-and-away round-robin matches. The top two teams of each group qualified for the 2018 FIFA World Cup, and the two third-placed teams advanced to the fourth round.
Fourth round: The two third-placed teams of each group from the third round played home-and-away over two legs. The winners advanced to the inter-confederation play-offs.
Entrants
The 46 FIFA-affiliated nations from the AFC entered qualification. In order to determine which nations would compete in the first round and which nations would receive a bye through to the second round, the FIFA World Rankings of January 2015 were used, as those were the latest published rankings prior to the first round draw. The FIFA Rankings of January 2015 were also used for seeding of the first round draw; however, for seeding in the second round and third round draws, the most recent FIFA Rankings prior to those draws were used.
Bye to the second round
Competing in first round
Schedule
The schedule of the competition was as follows.
The inter-confederation play-offs were scheduled to be played between 6–14 November 2017.
As a result of Indonesia being disqualified due to FIFA suspension, Group F contained only four teams compared to five teams in all other groups. Therefore, the results against the fifth-placed team were not counted when determining the ranking of the runner-up teams.
Third round
The third round consisted of two groups of six teams. The first two teams in each group qualified for the 2018 FIFA World Cup. The two third-placed teams proceeded to the fourth round. The draw for the third round was held on 12 April 2016, at 16:30 MST, at the Mandarin Oriental Hotel in Kuala Lumpur, Malaysia.
Groups
Group A
Group B
Fourth round
The two third-placed teams in each group from the third round played against each other home-and-away over two legs to determine which team advanced to the inter-confederation play-offs. The order of legs was announced during the draw for the third round. Syria played their home match, as with all their home matches in the third round, in Malaysia due to the war time condition in Syria.
Inter-confederation play-offs
The draw for the inter-confederation play-offs was held as part of the 2018 FIFA World Cup Preliminary Draw on 25 July 2015, starting 18:00 MSK, at the Konstantinovsky Palace in Strelna, Saint Petersburg. The fifth-placed team from AFC was drawn against the fourth-placed team from CONCACAF, with the AFC team hosting the second leg.
Qualified teams
The following five teams from AFC qualified for the final tournament.
