Abstract：In order to offer references for design of gob gas drainage with high-level long borehole，the laws of gob roof crack generation，fracture，fall and separation layer are analyzed with simulation experiment and key strata theory. Bending deformation of key strata undergoes the course of slowness→acuteness→slowness→fracture with the advance of working face，The bending and subsidence scopes of subordinate key strata are obviously smaller than those of major key strata. The elastic deformation of both side rock strata under key stratum will recover；and their subsidence will rebound after the fracture of key strata. Caving angles of roofs among key strata are different because of the differences of the load-bearing effect of key strata and mechanical characters of rock strata. The fracture of overlying key stratum results in decrease of the roof caving angle and the increase of periodic caving span and weighting intensity. The ultimate position and overlap distance of gas drainage boreholes can be determined based on fracture configuration of key strata，roof caving angle and periodic caving span，and gas drainage effect of boreholes can be also forecasted.
