The transport process of soil gas is pretty complex. It is influenced by many factors, which are influenced and restricted by each other. It has heavy spatial variation, and the spatial distribution and variation extent present very complex relationship with many factors. So it is very difficult to estimate the average conductivity of soil gas accurately in a large area when this happens in wild. This paper establishes a functional model about soil physical basic parameters and soil air permeability on the basis of data from measured soil samples. The results show that R2, the fitting degree of air permeability and water saturation, is up to 0.95 in sandy soil and more than 0.69 in clayed soil，because the clayed soil has higher soil structuralism. The fitting degrees of genetic algorithm system of the above two kinds of soil are more than 0.90. The absolutely relative error between the fitting air permeability and the measured air permeability is less than 0.1 by using this functional model. Furthermore, this functional model proves applicability and has good effect. The proposed method simplifies complicated calculation process of practical application and provides reference to gain soil gas transportation dynamics parameters quickly and easily.