Abstract: The accumulation of gas at the corner of a U-shaped working face has always been an important factor that restricts the safety production of coal mines, in order to improve the extraction rate in the goaf and reduce the gas concentration in upper corner, the 22115 working face in Luning coal mine is used as the background, the development height of roof fissure zone and the optimal parameters of high boreholes in upper corner are studied by using the method of theoretical calculation, numerical simulation and field testing.The results show that the optimal placement of the final hole is at the junction of tensile zone and closed zone, the highest development height of fracture zone of Luning coal mine is 59 m, and according to the field test, the optimal height of the end hole location of the high level borehole is 45 m.