According to the structural characteristics of frame of large wheel tractor, a spatial mechanism multi-body system model with eight degree of freedoms was set up. In order to obtain solutions of multi-bodies dynamic simulation, the augmented formulation based on Euler 4 parameters was set up and simulation programs of multi-body dynamics were developed with help of Matlab software. The elasticity of tires in longitudinal and lateral direction was described with a spring-damper element of variable parameter in series. In the program the iteration equations of the tires functions and hydraulic cylinders functions with a dynamic pressure feedback network were calculated to reveal the nonlinear relations between the force with displacement and velocity of the tractor bodies. Multi-body dynamics simulation of the model was carried out to obtain dynamical loads and vibration frequency. The adaptive ability to environment and safety of steering could be improved by using a dynamic pressure feedback network in hydraulic system of steering. 