The sorption isotherms and vapor permeability of autoclaved aerated concrete are obtained with the static gravimetric method and the cup method at 15℃, 25℃ and 35℃, respectively. The approaoh to determine value of variable permeability has been discussed. Meanwhile, it has been compared with the fixed value in Thermal Design Code for Civil Building (GB 50176-93). The results show that temperature dependence of the sorption isotherms and vapor permeability of autoclaved aerated concrete is small within test temperature range. Moreover, for adsorption process in medium or whole RH range, the average permeability obtained from our method is almost the same as that in the Code. This method can be extended to other porous building materials to obtain accurate permeability throughout whole RH range for both adsorption and desorption processes.