The designed mining thickness of 30101 working face of Hamogou Mining Industry Corporation Ltd. is 2.5 m， in order to study fracture zone of overlying strata after mining， fracture zone height of overlying strata was settled by UDEC numerical simulation. The model size set by UDEC is 200 m×140 m， the fracture zone of the working face was conducted by simulation analysis， the fracture development height was stable after working face advancement of 20 m， the height was 30 m by numerical simulation， the height after mining was calculated as 41.6 m， both of the result by calculation and numerical simulation verified each other， and the height was settled as 41.6 m at last.