Abstract: This research aims to develop a new method for predicting the water activity and moisture content of cigarettes after packaging. First, the isothermal absorption curves of different materials are plotted, and the GAB model is used for fitting to establish the corresponding isothermal equations. Then, based on the principle of constant total moisture content and consistent water activity among various components after equilibrium, this method can successfully predict the water activity and moisture content of cigarettes after packaging. The results show that within the range of water activity from 0.2 to 0.8, the GAB model can effectively simulate the isothermal absorption curves of cut tobacco, filter sections, and boxes of four different types of cigarette packs, with the R² values all greater than 0.980, and the relative deviation of the predicted water activity and moisture content of the cut tobacco after packaging is less than 4%. Therefore, this method has high accuracy in predicting the water activity and moisture content of cut tobacco after packaging, providing guidance for the moisture design of cigarette and packaging materials. At the same time, it provides a theoretical basis and methodological support for reducing the migration from cut tobacco moisture to packaging materials and for stabilizing and maintaining the moisture of cigarettes.