Abstract: In order to determine the reasonable length of the mining face for high strength fully mechanized caving mining in low gas seams, taking 42108 fully mechanized caving face of Buertai Mine as the research object, the formula of checking the mining face length with ventilation capacity is deduced, and the gas movement laws under different mining face lengths are simulated by Fluent numerical software. The results show that the difference of coal cutting and coal caving recovery rate should be fully considered in the derivation of the formula for checking the length of mining face with ventilation capacity. There is a critical value between the length of the mining face and the amount of gas emission. When the length of the mining face exceeds the critical value, the gas emission will pose a great threat to the safety production of the mining face. Combined with theoretical calculation and numerical simulation results, the reasonable length of 42108 mining face is finally determined to be 310 m.