In order to reduce the water absorption of autoclaved aerated concrete(AAC), three types of water repellent were added into AAC and its effect were observed. The compressive strength, thermal conductivity and water absorption of AAC containing potassium trimethylsilanolate(PT), calcium stearate(CS) and siloxane based polymer(SP) were tested. The experimental results indicate that the water absorption of AAC is reduced greatly with the addition of three types of water repellent and the strength retention coefficient(RS) is significantly improved as increasing the content of water repellent. The testing results show that, among three types of water repellent, addition of siloxane based polymer is the best and the content(by mass) of 04%08% is recommended.