Abstract: In order to study the influence of the variation of atmospheric pressure change on the gas accumulation in the unsealing coal mine fire zone, to explore a reasonable time to unseal and reduce the risk of it, the state of gas in the closed fire area was calculated by Fluent software based on the mechanism of atmospheric pressure on gas migration in fire area, which was in the process before opening coal mine fire zone and after opening coal mine fire zone, and the state of gas in each period of unsealing of coal mine was analyzed. The results show that when the atmospheric pressure changes slowly, the risk of unsealing of fire zone is in low level. During the process of unsealing of fire zone, the oxygen concentration near the fire zone is higher when the airtight distance is closer to the fire zone because of the continuous leakage of fresh air from outside into the closed zone. Gas accumulation mainly at the downwind side of the ignition zone, and the gas concentration decreases with the increase of oxygen leakage into the fire zone. In practice, according to the actual situation of the mining area, the unsealing time should be selected reasonably; the gas state in the fire area should be monitored at all times, so as to improve the safety of the unsealing of coal mine fire area.