In this paper, the chassis frame of a soybean harvester is taken as an object. Using three-dimensional modeling software Solidworks for the parametric modeling and finite element before the import processing software Hypermesh for the finite element meshing and modal simulation analysis of the chassis frame the modal test of frame samples is conducted to verify the validity of the simulation results.The strength of the chassis under different working conditions is checked and calculated. With the maximum allowable stress of the material taken as constraint when the natural frequency and dynamic load coefficient of the chassis are 2.5, and with the minimum weight of the frame taken as the target, the lightweight optimization design is carried out and the mass of the chassis after optimization is reduced by 16%.