Abstract: In order to reveal the essential mechanism of adsorption-desorption hysteresis of CH4 and CO2 in coal，the adsorption-desorption behavior of CH4 and CO2 in coal is studied from the molecular scale by using the combination of grand canonical Monte Carlo and molecular dynamics simulation.A complete adsorption-plastic deformation-structure hysteresis-adsorption hysteresis mechanism chain is established by systematically analyzing multi-dimensional data such as adsorption configuration，pore structure，ener⁃ gy distribution and adsorption thermal evolution.The results show that gas adsorption can induce significant plastic expansion of coal matrix，and this structural deformation is irreversible in the desorption process. CO2 can induce more significant plastic deformation of coal matrix than CH4，which not only makes it have higher adsorption capacity，but also leads to a wider adsorption-desorption hysteresis loop.During the de⁃ sorption process，the plastic deformation-locked pore structure and deep-level adsorption sites greatly en⁃ hance the retention capacity of CO2. Therefore，the traditional rigid structure model has some errors in studying the adsorption behavior of coal to CH4/CO2 gas. By introducing a flexible model，the adsorption be⁃ havior of coal to gas can be more perfectly revealed.

Key words: coalbed methane mining, adsorption-desorption, molecular dynamics, adsorption expan? sion