The combination of two lightweight methods, topology optimization and lattice filling, makes lightweight design have infinite possibilities, and additive manufacturing technology makes it possible to manufacture, which greatly promotes the possibility of its development and application. Two lightweight methods of topology optimization and lattice filling were combined to carry out lightweight design of automobile bearing support. Simp-stiffness material density interpolation model was established by using variable density topology optimization technology to optimize the material density distribution of bearing support, and three relative density intervals of 0-0.4, 0.4-0.8 and 0.8-1.0 were divided. The body centered cubic lattice structure with the relative density of 0.2, 0.6 and 1.0 was used to fill the three relative density interval regions, and the lightweight automobile bearing bearing was assembled and integrated. The finite element analysis of its safety performance show that the overall stress and strain gradient of the lightweight bearing is uniform, the material utilization rate is improved, and the maximum stress is changed from 215 MPa of the original model to 356 MPa, which still meet the use requirements. Compared with the original model, the mass is reduced by 53.89% to achieve lightweight effect. This design idea can provide an effective and practical new method for the lightweight of mechanical structures in the fields of aerospace, automobile and ship.