【Objective】The isotherm of soil water vapor adsorption is one of the basic hydraulic characteristics of soil. Simulating the isotherm accurately is of great significance to studying mechanism of the interaction between soil and water molecules and predicting migration of volatile organic gases in soil. 【Method】In this study, seven typical soils of different regions of China were collected for determination of water vapor sorption isotherms with vapor sorption analyzer, separately, in lab. During the process, the water activity of the sample was controlled with the range of 0.1~0.9, and temperature was at 25 °C. Then the GAB (Guggenheim-Anderson-deBoer) model was used to evaluate effect of the simulation of water vapor sorption isotherms, and its performance was evaluated by root mean square error and determination coefficient. Factors influencing factors of water vapor adsorption behavior and mechanism of the interaction between water molecules and soil particles were discussed. 【Results】For simulation of water vapor adsorption and desorption curves of the seven types of soils investigated, the root mean square error of the GAB model was lower than 0.000 7, while the determination coefficient was higher than 0.995. Compared with the soil water vapor desorption process, the monolayer water adsorption during the water vapor adsorption process was quite lower, but the molecules free enthalpy of pure liquid water and single-layer adsorbed water was rather high. Monolayer water content during the adsorption and desorption processes and hysteresis index were ultra-significantly and positively related to the organic carbon content. Monolayer water content was higher during the desorption process (M₀ = 0.002 8~0.031 4) than during the adsorption process (M₀ = 0.001 2~0.023 0) in the seven types of soils. The relation of monolayer water content with clay content was affected by type of soil mineral. And no significant relationships were observed between soil physico-chemical properties (such as organic carbon content, clay content and so on) and other GAB model parameters (for instance,C, K ) during the adsorption and desorption process. 【Conclusion】The GAB model is proved to be able to accurately describe water vapor adsorption and desorption processes in the investigated soils. Soil water vapor sorption capacity is highly affected by soil organic carbon content, clay content and type of soil mineral. Hysteresis occurred in all the investigated soils, and varies with soil physico-chemical properties.