This paper presents a mathematical model for multi-axle vehicles Inclusive of steering system, suspension system, tire model, body system. Considering possible factors related to turning motion such as vehicle configuration and suspension, equations of motion were constructed to predict steerability and stability of these vehicles. Turning radius, slip angle at the mass center, and each wheel velocity were obtained by numerically solving the equations. The simulation model is made by MATLAB based on the mathematic equation. To analyze the influence of the wheelbase layout on vehicle stability, driving performance and stability of the vehicle with three wheelbase layout is simulated based on the present model. It is concluded that the wheelbase between second axle and third axle should be long to get better stability when vehicle turning with rear axles.