Seventeen of the aircraft will come from the group's backlog with Airbus, said chief executive Tony Fernandes, with the remainder leased in.
The group will take the first three A320s in the first quarter, with one each for its Malaysian, Thai and Philippine operations, said the group in its full-year financial statement.
AirAsia Thailand's fleet will grow by a total of two aircraft in the first half, with the new aircraft used to launch five new routes and increase frequencies on "other strongly performing sectors".
Its Indonesian associate airline, AirAsia Indonesia, will launch three new domestic services - Bandung-Surabaya, Surabaya-Denpasar and Jakarta-Semarang - in the first quarter of 2012.
"These new routes form part of the IAA strategy to re-enter the Indonesian domestic market which has high growth potential given the rapidly rising incomes of the Indonesian middle classes," it said.
Frequencies will also rise on the existing routes from Jakarta to Denpasar and Penang. Two further routes will be launched from Malaysia to Semarang in Indonesia and Surat Thani in Thailand.
Operations will begin at its Philippine associate in March or April, said the carrier, following the grant of its operator's licence, with AirAsia Japan to follow in the second half of 2012. The latter represents "a significant [low-cost carrier] opportunity" given the low penetration of low-cost carriers in the market, said Fernandes.
"Our proven track record and strong brand of low fares shall pave the way for exponential growth in both markets," he said.
Forward bookings for the three operational airlines show passenger demand "remains positive". January load factors fell slightly in Thailand and Indonesia, against the same period a year earlier, while Malaysia showed a load factor increase.
Average fares were higher in all three countries, it added.
AirAsia Thailand and AirAsia Indonesia remain on course for their IPOs this year, said Fernandes.