Many simulation software to predict thermal environment of buildings, such as temperature, humidity, heating and cooling load of building spaces, have been developed according to the development concept such as calculation accuracy, calculation speed, user-friendliness. However, most of them do not take into account moisture transfer in wall assemblies. Humidity calculation in most software is simply affected by ventilation and focuses on just the building spaces. A Heat, Air and Moisture (HAM) simulation software called THERB has been developed for the purpose of estimating the hygrothermal environment within buildings. This software has complete HAM features including principles of moisture transfer within walls. In this paper, the prominent features of the THERB are highlighted. Then the accuracy is verified through the comparison of calculation and monitoring results of a residential building. The difference of hygrothermal environment is clarified based whether or not moisture sorption and desorption of walls are incorporated. Furthermore, Sensitive analysis utilizing THERB is performed with the differences of calculation models on heat transfer and incident solar radiation into indoor surfaces.