Abstract: Tongxin Coal Mine uses fully mechanized top coal caving to mine flammable special thick high gassy seam, and 8106 fully mechanized caving face is at lower old fire zone in Meiyukou Coal Mine, and a large amount of CO gas is discharged in mining process, which causes serious overrun of CO gas at working face. The mine takes pressure balancing ventilation technology to effectively prevent and control CO gas overrun at working face, and adopts a method of injecting mass flow nitrogen by high level drilling in the goaf to form a gob of three-dimensional nitrogen flow, which eliminates the hidden that the gas in goaf may ignite by upper old fire zone.