Abstract: Theef fects of the primary vertical suspension on the dynamic mechanics of heavy haul freight cars were analyzed by simulation to decrease dynamic wheel/rail interactions through optimizing the parameters of the primary vertical suspension.The vehicle-track coupling dynamics and the method of optimal matching design were applied int he simulation.The simulation results in dicated that the primary vertical stiffness had little effect on the dynamic wheel/rail interactions; when at highvalues,the primary vertical damping decreased the vibration soft racks tructure,but increased those of carbody;and the prefer able primary vertical damping was5 0500kN·s/m.