Abstract: In order to quickly and accurately determine the separated layer displacement of the overburden strata above the coal mining face during the seam minin g process and to guide the implementation of the surface gas drainage borehole drilling protection project, the combination of the surface subsidence law and the combi ned key layer theory were applied to analyze the cause of the separated layer displacement of the overburden strata above the coal mining face under the mining influe nces and to establish an experience calculation method to calculate the separated layer displacement of the overburden strata above the coal mining face.With the num erical simulation, the calculation method was verified and was applied to the trial on the surface gas drainage borehole drilling project of Chengzhuang Mine, Jincheng Coal Mining Group.The results showed that the separated layer displacement size of the overburden strata above the coal mining face would be dependent on the subsi dence displacement differences between the top and low combined key layer of the separated layer interface. The distribution law of the separated layer displacement al ong the inclination direction of the coal mining face would have a high peak in the middle of the coal mining face and would have a variation law getting small from the middle of the coal mining face to the ends of the coal mining face.The borehole layout of the surface borehole drilling would be suitable to be selected in the area betwe en the subsidence turning point of the coal mining face and the coal mining face boundary.