Li Hailong transient-flow model in measuring air permeability doesn’t need to measure the gas flux through the samples. The measurement time is short and exerts little damage to the sample structure compared to the traditional steady-state measurement, but the key parameter s of the transient-flow model which describes the pressure-time relationship in the air chamber needs lots of calculations, causing inconvenience in their application. Therefore, this paper tried to simplify the calculation process of parameter s based on Li Hailong transient-flow model and then tested it by steady-state method. Through the 40 soil sample’s measurement indoors, the outcome indicated that the relationship between and the time t was similar to the transient-flow modle linear relation raised by Kirkham. Furthermore, if taking parameters s as a standard, the relative error range of Parameters s and simplified solution s0 was under 0.5%, and the relative error as a whole was very low.