The multi-body system spatial model with 12-DOF concerning in-situ steering of the articulated tractor was set up with the augmented formulation based on Euler Four Parameters. The mathematical models of the hydraulic steering system of large wheel tractor were set up with state space method by 12 parameter varieties. The simulation programs of multi-body dynamics and hydraulic system were developed with help of Matlab software. In-situ experiments on rigid road were carried out, and the steering multi-body system model was validated by the experimental results. Dynamic characteristics of in-situ steering of the tractor were obtained, and it will be beneficial to the subsequent research on the steering by wire system and automatic driving technology of this type tractor. 