Abstract: The change of external environmental pressure is one of the main factors affecting the gas desorption pattern of coal samples. In order to study the difference of gas desorption under atmospheric pressure and step-down pressure, we conducted the experiments of atmospheric pressure desorption and step-down pressure desorption on coal samples under different adsorption equilibrium pressures by using the self-developed gas-bearing coal desorption system, to compare and analyze their desorption characteristics and summarize the applicability of different empirical formulas to the desorption data. The results show that: the gas desorption volume in both desorption environments shows a “rapid rise - slowing down - stabilizing” with time; in the process of step-down desorption, the gas desorption volume in the same desorption time increases as the desorption pressure decreases, and the desorption takes longer time to reach the equilibrium state. In the process of stepwise desorption, the amount of gas desorbed in the same desorption time increases with the decrease of desorption pressure, and the time required for desorption to reach the equilibrium state becomes longer, and the accumulated gas desorption volume at different adsorption equilibrium pressures is negatively correlated with the desorption pressure.