In order to solve the non-coaxial problem of electric rear axle and reduce environmental pollution, the lightweight design of electric rear axle is carried out. A novel coaxial integrated electrical rear axle system is proposed in this paper. The strength and stiffness simulation is analysed under four kinds of limiting operational conditions. Based on the finite element analysis results, an electric rear axle housing lightweight optimization model is established with the axle thickness as the design variables and the axle housing quality as the objective function. Goal-driven optimization scheme is used to solve the optimization model, and the response relationship between the axle thickness and the maximum displacement, maximum stress and the total mass is analyzed. The simulation analysis about the optimized electric rear axle is done based on the four kinds of limiting operational conditions, and the results show that the electrical rear axle reduces its weight by 8.4% compared with that before the lightweight, meeting the requirement of electric drive rear axle.