Considering road characteristic parameters such as lateral gradient, longitudinal gradient and synthetic gradient, and based on 15 degrees of freedom (DOF) vehicle dynamics model, the authors develop the vehicle dynamics model, tire vertical load variation model and whole vehicle riding dynamics simulation model combined with steering system, braking system, power train system, wheel and suspension models. The situations are compared under different lateral, longitudinal, synthetic gradient and vehicle speed. The simulation results show that yaw rate maintains invariably to longitudinal gradient variation, but decreases gradually with the increase of lateral and synthetic gradient. The margin of fluctuation and peak value increase with the increase of vehicle speed under the same gradient; front wheel sideslip angle maintains invariably to longitudinal and synthetic gradient variation, yet increases with the increase of lateral gradient; the roll rate decreases and then increases with the increase of lateral and synthetic gradient, and the margin of fluctuation and peak value increase with the vehicle speed increase under the same longitudinal gradient.