The body frame of a combine harvester was used to build the body frame geometry model.As the complexity of the body frame structure of the harvester,the road motions,cutter excitation,threshing roller excitation and other vibration generated by the body frame will be passed to the driver.In order to simulate the process of vibration excitation to the human body frame in a more appropriate way,it is necessary to soften the harvester body frame that conducted the vibration excitation.Based on the geometry model,the finite element soft body frame analysis is used to establish the finite element soft body frame model of the vehicle body frame.The modal analysis and calculation are carried out on the basis of the new model.In the structural vibration,the influence on the dynamic behavior of the structure of lower order mode is more than that of the higher order mode.The low order mode determines the dynamic characteristics of the structure.The body frame structure was optimized with the first-order mode.The results showed that the first-order modal frequency of the body frame of 7.29 Hz is close to the excitation frequency (7 Hz) of the cutter when the harvester works normally,which is prone to resonance and has the greatest impact on human comfort.In order to adjust the natural frequency of the body frame of the harvester to avoid the external excitation frequency range,the size and topology of the model of the vehicle body frame were optimized with HyperMesh software.The results showed that the first-order modal frequency of the harvesting machine body frame upgraded to 8.63 Hz from the 7.29 Hz.The body frame mass decreased by 0.006 t after the size optimization.After topology optimization,it was the same that the first-order modal frequency of the harvesting machine body frame was improved to 8.49 Hz from 7.29 Hz.The body frame quality was reduced by 0.107 t.The natural frequency of the harvester body frame can avoid the external excitation frequency range by optimizing topology and size.Considering the goal of design optimization and manufacturing cost,the size optimization technology is more suitable.It will provide some reference for reducing the probability of occurrence of body frame resonance and the optimizing lightweight and comfort of harvester to a certain extent.