Abstract: To reveal the law and mechanism of high level boreholes in gob controlling gas overrun in fully mechanized coal face, taking W1308 fully mechanized coal mining face of Sihe Coal Mine in Jincheng Coal Group as the research object, the UDEC software was used to determine the high level borehole layout layer. The seepage model of heterogeneous gob with the gap distribution characteristics of “O” type ring was established by using the further development tools of UDF. Based on the idea of source prediction, the accurate calculation model of gas emission source in the gob was established. Finally the CFD model of gas storage and migration in the gob of W1308 fully mechanized mining face was formed. The gas pressure field and gas concentration field under the action of high borehole were simulated and the mechanism of the high level borehole in gob efficiently controlling gas overrun was revealed, and the optimum negative pressure of the hole was 26.3 kPa. The relative error of the field measurement and the simulation result was less than 10%, and the numerical simulation method could be used to predict the gas drainage effect by high level borehole. The results showed that when other conditions are certain, the gas concentration in the upper corner and the gas concentration in the return air lane decreased first and then increased with the higher negative pressure of the high level borehole, and the optimum negative pressure existed.