Abstract: Gas is the biggest threat to coal mine safety,and gob gas is one of the main sources of mine gas. In order to master the law of gas distribution in gob of fully mechanized mining face under U-ventilation,taking Xinjing Mine 3213 as research object,FLUENT software is used to simulate the gas distribution in gob of fully mechanized mining face under U-ventilation.The results show that the gas in the gob has significant distribution characteristics in the plane and vertical directions due to the influence of ventilation,air leakage,gas density and the characteristics of pores and fissures in the gob. On the plane,the gas concentration in the air inlet way is lower than that in the air return way,and the gas concentration increases gradually toward the far end,and the gas concentration locally accumulates in the upper corner. In the vertical direction,the gas concentration is generally high in the upper part and low in the lower part. The research results have important theoretical guidance and practical significance for gas extraction and control in the gob of U-type ventilated fully mechanized mining face in the study area and adjacent mining areas with similar geological conditions.