In view of the characteristics of complex overburden structure and strong mining pressure in deep coal seam working face with large mining height, taking Yangchangwan Coal Mine as the engineering background, the mechanical model of overburden rock structure in Yangchangwan Mine with large mining height is established by using theoretical analysis, similarity simulation and field measurement, and the comprehensive research is carried out on the fracture of overburden rock structure and the working resistance of hydraulic support in fully mechanized caving face with large mining height. The results show that during the normal mining period, before the basic roof reaches the limit caving distance, the direct roof and part of the basic roof break cannot fill the goaf, so that the inverted step “cantilever beam” structure is formed above the working face, and the hydraulic support is mainly used to prevent the cantilever beam structure from rotary instability; during the period of pressure, the basic roof and the upper two rock strata break and collapse to fill the goaf, and a “masonry beam-cantilever beam” structure is formed above the working face. The hydraulic support provides the pressure to prevent the rotary instability of the direct roof “cantilever beam” structure, and the pressure to prevent the rotation of the basic roof “masonry beam” structure.