Taking a crawler joint harvester chassis frame as the research object, a 3D frame model was built, importing the model into Ansys Workbench to establish a finite element model, and conducting modal analysis and taking the wall thickness of the frame as the design variable, the frame thickness as the research variable, frame multi-objective optimization was carried out. Under the premise of meeting the performance parameters, calculate the best frame wall thickness, improve the accuracy and efficiency of optimization, genetic algorithm was used to optimize multi-objective optimization of beam thickness. The results showed that under the verification of the stiffness, strength and modal characteristics of the chassis frame, the high-strength steel composite frame reduces the 36.1Kg, weight reduction effect by 11.1% compared with the original frame quality, and the lightweight effect is significant.