Abstract: Gas drainage in goaf by surface L-shaped boreholes can not only reduce gas accumulation in upper corner of working face, but also facilitate the utilization of gas drainage. It has been experimentally applied in many mining areas in China, and the gas control effect and economic benefit are remarkable. However, there is a certain gap between the gas drainage effect of some surface L-shaped borehole and the expected drainage target. In order to improve the gas drainage effect of L-shaped boreholes, based on the "three zones" theory of stope rock movement and the gas migration law of working face, this paper comprehensively analyzes the influencing factors of L-type borehole pumping goaf gas, and studies the adaptability of L-type borehole and the optimization of horizontal section position of L-type borehole. The results show that the surface L-shaped borehole gas extraction technology is suitable for high gas working faces with high proportion of goaf emission, U-shaped ventilation and overhead mining face, and large amount of gas resources in goaf. The horizontal section of the L-shaped borehole should be arranged close to the side of the return air roadway of the working face. In the vertical direction, the starting point to the final hole point should have a certain downward dip angle, and the height of the starting point and the final hole point should be located in the upper and lower parts of the fracture zone respectively. In the horizontal direction, the horizontal section of the L-shaped borehole should be located in the fracture development area and close to the boundary of the return air side as far as possible. At the same time, the calculation methods of the vertical distance between the starting point of the horizontal section of the L-shaped borehole and the coal seam floor and the horizontal projection distance from the return air roadway are given respectively.