Abstract: An optimal design method based on multi-objective genetic algorithm NGSA-II and parameterized model was proposed to achieve lightweight of the differential case of a new energy vehicle while meeting the rigidity and strength requirements of driving conditions. Through the joint simulation of SolidWorks and ANSYS, the thickness of the big end, the small end, the flange, the outer circle of the main reducer and other parts of the differential case were firstly parameterized, and it was proved that the differential case had enough optimization space through modal analysis and static calculation. Secondly, a response surface between size variables and optimization objectives was constructed. Finally, based on the multi-objective genetic algorithm, the optimization model aiming at minimizing the mass and the maximum stress on the case was established to realize the lightweight design of the differential case. The results show that the total mass of the optimized case enjoys a mass reduction by 10.3% (from 6.80 kg to 6.10 kg); the maximum stress on the case is reduced by 9.9%, and the maximum deformation of the case is within the safe range. The above results prove that it is feasible to carry out lightweight design based on multi-objective genetic algorithm.