This paper investigates the dynamic characteristics and fatigue robust optimization of heavy-duty tractor. First, this paper presents a vehicle model with sub-structure method. Based on the theory of base motion, the structure dynamic characteristics are analyzed. Second, the accuracy of the method is verified by comparing the experimental results with the simulation results. Also, the dynamic response and the transfer function of vehicle are obtained using the above methods. Combined with the experimental data, the methods of random multiple frequency components and multi-axial fatigue life are adopted to analyze the fatigue damage of the heavy-duty tractor under different road conditions. Finally, the Design for Six Sigma is used to optimize the vehicle’s structure. The results show that by using the proposed method, the dynamic characteristics of the vehicle can be analyzed accurately and effectively, robustness of the vehicle can be improved, and mass of the vehicle can be reduced.