In this paper, a forward classification optimization design idea for the subframe structure with discrete material distribution and take a typical subframe of a dust suppression vehicle is taken as an example to optimize and verify. Using the finite element method, we established a simulation model for the dust suppression vehicle, and the feasibility of lightweight design was determined through the multi-condition stress analysis and modal analysis of the subframe structure of the model. Firstly, the water tank bracket structure is taken as the topology optimization space, the compromise topology optimization based on grey correlation is carried out, and the conceptual design is carried out according to the material distribution of the water tank bracket shown in the topological cloud image. Then the response surface optimization model is established, and the thickness of each structure of the subframe is parameterized. Before optimization, a Pareto graph was drawn through sensitivity analysis to exclude variables with weak correlation with optimization objectives, and a high-precision response surface was fitted by least square method to meet the requirements of response surface model adaptation. Finally, the best solution was found by GRSM algorithm. After adjusting the original model according to the parameters of the best solution, the optimized subframe not only meets the operational requirements of the dust suppression vehicle but also achieves a 23.8% reduction in weight, demonstrating significant practical engineering value.