Abstract: For revealing mechanical mechanism of roof staging damage caused by weak interlayers, numerical simulation is adopted to reveal the deformation and failure laws of composite roof which contains the weak interlayers (coal lines). Failure structure model of composite roof is established to determine mechanical conditions of composited roof, and it is proved by field test. The results show that the damaged weak interlayer is the key element for roof deformation and fracture; the process of the composite roof deformation and fracture can be broken down into three stages that fixed end beam, laminated composite beams, combined three-hinged arch; the composite roof can be damaged and turned into combined three-hinged arch when the yield span of each rock is less than actural span of composite roof.