The metal baler is a largescale core engineering equipment in the scrap metal recycling industry. In order to improve the overall performance of the metal packing case body structure and achieve the goal of lightweight box body, a lightweight design method based on response surface methodology was proposed. Based on plate and shell theory and mechanical model analysis, a finite element parametric model of the dangerous working conditions was established, with wall thickness and other dimensions as design variables, structural strength, rigidity and stability as constraints, and box weight as objective function. Sensitivity analysis was used to determine the design variables that had significant effects on the objective function, and then the central composite design method and Kriging interpolation method were used to obtain the fitted response surface model, and the multiobjective genetic algorithm was used to optimize the response surface model. The results show that under the condition of meeting the overall comprehensive performance of the cabinet, the weight of the optimized cabinet is reduced by 20.6%, and the optimization effect is significant, which has certain guiding significance for the lightweight design of other engineering equipment.