In order to improve the lightweight optimization effect of commercial vehicles, a certain flat-head commercial vehicle cab is used as the research object to establish a geometric model of the commercial vehicle cab. Through stiffness calculation, bending deformation of the cab longitudinal beam and calculation of the windshield door frame Deformation analysis to evaluate the stiffness performance of the cab model. A free modal analysis is carried out, with the Z-direction displacement under bending conditions and the first-order torsional natural frequency not being less than the initial value as constraints, and the minimum cab weight and torsional deformation as the optimization objectives. The 16 selected products were screened by relative sensitivity analysis. The thickness variables are optimized for design, and the NSGA-II genetic algorithm is used for multi-objective optimization, and the solution that meets various performance requirements and has smaller quality is selected as the optimized solution. The optimization results show that while the cab weight is reduced by 13kg, the stiffness performance is significantly improved, with a weight reduction rate of 3.44%, and the optimization effect is significant.