In order to study the isothermal adsorption characteristics for cut tobacco, cut stem and cut reconstituted tobacco, the adsorption hysteresis was quantified using the definite integral expression of GAB model, and the isosteric adsorption heat of the adsorption and desorption process to characterise the binding capacity of water and cut tobacco samples was analysed by Clausius-Clapeyron equation. The relationship between the difference of isosteric adsorption heat, adsorption hysteresis and equilibrium moisture content was analysed. The results showed that: 1) Under the same adsorption temperature, the adsorption hysteresis of cut tobacco was the largest, followed by cut stem, and the adsorption hysteresis of cut reconstituted tobacco was not significant. 2) With the increase of adsorption temperature, the adsorption hysteresis of cut tobacco and cut stem weakened and adsorption hysteresis content decreased. 3) The trend of isothermal adsorption heat of different tobacco blend formulations was significantly different. With the increase of adsorption quantity, the adsorption heat of cut tobacco decreased rapidly at first and then tended to the heat of water vapor liquefaction, while that of cut stem and cut reconstituted tobacco increased slowly at first and then tended to the heat of water vapor liquefaction. 4) The difference of initial adsorption heat between the desorption process and the adsorption process is significant, and the larger the difference of adsorption heat, the more significant the hygroscopic hysteresis. The thermodynamic causes of adsorption hysteresis of cut tobacco and cut stem are also analysed by this method.