Aiming at the problem of the failure of the automobile seat belt retractor, the composite emergency locking automobile seat belt retractor is taken as the research object, and the working principle and failure form of the automobile seat belt retractor are introduced. By analyzing the reasons for the failure of the car seat belt retractor, a structural optimization design plan to solve the deformation of the car seat belt retractor bracket and the fracture of the mandrel is proposed. Using HyperMesh finite element software analysis, with the goal of lightweight, the stress value and strength value of the automobile seat belt retractor structure are analyzed. The comparison standard shows that the structure meets the performance requirements, reduces the cost of post-production samples, improves economical and technical efficiency, and provides a reference for the design of car seat belt retractor.