The cage occupancy plays a crucial role in the thermodynamic stability of clathrate hydrates and is an important quantity for understanding the CO2-CH(4 )replacement phenomenon. In this work, the occupancy isotherms of pure CH4, pure CO2, and their mixture in sI and sII hydrates are studied by GCMC + MD simulations. The adsorption of CH4 and CO2 + CH4 in the sI and sII hydrates can be categorized as the one-site Langmuir type. The calculated occupancy ratio theta/theta s and the abundance ratio of CO(2 )to CH4 vary with the temperature and pressure, which provide the prerequisite information for the prediction of CH(4 )recovery yield at different conditions in the CO2-CH4 gas exchange process. The phase equilibria of clathrate hydrates pure gases and mixtures are explored and the corresponding heat of dissociation and hydration numbers are determined. The current investigation provides new perspectives to understand the mechanism behind the gas adsorption behavior of clathrate hydrates.