Abstract: The automobile reinforcement plate produced by a company cracked before final assembly, whose material was 22MnB5 hot stamping steel with Al-Si coating. The failure reason was analyzed by fracture morphology and microstructure observation, and chemical composition and hardness tests. The results show that the fracture mode of the failed reinforcement plate was a mixture fracture of ductile and brittle. The corner radius was relatively small during laser trimming blanking, leading to the crack initiation at the edge of trimming. The cracks propagated rapidly along the bending deformation region without laser trimming under the impact load during transport. By increasing radius at the corner and all-round laser trimming of the reinforcement plate after stamping, the indentation on the coating of the reinforcement plate became shallow before final assembly, and no cracking occurred.