Abstract: For the purpose of deeper investigation on vibration problem of human-tractor system, and based on the structural characteristics of the human and the tractor, a human body is modeled as a nonlinear mechanical system, and a nonlinear multi-freedom-degree vibration model for the human-tractor system is derived in this paper. The simulated results, obtained from a numerical example and compared with the experimental values, show that the vibration model is valid. This research provides a theoretical basis for the future study on the numerical simulation technology for designing the tractor with the best driving comfortablity.