Abstract: The roof stress state,failure mode and change amplitude of mining vertical stress have been studied in the course of 68303 fully mechanized working face mining in Du Er-ping mine by method of FLAC^3D numerical simulation based on the mechanical properties of rock mass and rule of defromation and failure. The roof two-zone's height was analyzed and presumpted by extracting the field data and information of roof tensile and shear,plastic deformation and change amplitude of mining vertical stress. The result of comparative analysis showed that the roof two-zone's formation mechanism and the heights can be basically reflected by the numerical simulation result of stress state,failure mode and change amplitude of mining vertical stress. The conclusion shows that numerical simulation as the method of deciding fully mechanized working face roof two-zone's height is feasible.