Abstract: In order to solve the problem that under U type ventilation the gas concentration in the upper corner of the fully mechanized caving face was overrunning due to gas emission of the left mine in gob, the CFD bistable computing model of gas emission of the left mine in gob was builded.and By numerical simulation method the air-flowing field and the gas-concentration field in gob under U-tube ventilation system, U+I-tube ventilation system, inclined to Y type ventilation system and Paratactic double U-shape ventilation system were simulated. With different air quantity of coal face, gas-concentration in upper corner, gas-concentration in return airway, gas-concentration in the wind drainage roadway in the gob and total gas quantity of air-flow were analyzed and compared. The results showed that under U+I-tube ventilation system, inclined to Y type ventilation system and Paratactic double U-shape ventilation system, the gas-concentration in upper corner was well controlled, but gas-concentration in the wind drainage roadway in the gob had a high probability of exceeding the limit. The research results had important reference value for controlling gas emission of the left mine in gob by air quantity of the fully mechanized caving face.