The relation between the equilibrium moisture content and the water activity of crust filling at 23, 30 and 45 ℃ were studied by gravimetric method. The test data were fitted with some typical moisture absorption models by Matlab. The results showed that the moisture isotherm of crust and filling were both S type model. When the moisture activity was constant, the equilibrium moisture content first increase and then decrease with the increase of temperature, which was different from other foods. The Lewicki model and Peleg were the most suitable for fitting adsorption isotherms of crust and filling when the moisture activity was between 0.35 and 0.90. According to the isothermal hygroscopic characteristic model theory of multi-component food, a combined model was developed to characterize the isothermal hygroscopicity of the rice made wafer.