Abstract: In order to find the reason for gas concentration decreasing little and the amount of gas through ventilation increased in the working face of return airflow roadway after ventilation system adjustment in NO.10416 working face of Yangliu Coal Industry Company, it analyzed the changes of ventilation facilities and mining situation, and their effects on the amount of gas by ventilation and goaf leakage of NO.10414 working face since the ventilation system adjustment. Through the analysis, it obtained the influence factors, which included the variation of air-volume and ventilation resistance caused by ventilation system adjustment, the influence of temporary ventilation installation, the effect of neighbor local fan in the return airflow roadway of NO.10414 working face, the changes of mining condition and so on. The main reasons were the ventilation system adjustment and local fan in the return airflow roadway of NO.10414 working face.