Based on the vehicle/track coupling dynamics theory, analysis and compae the  dynamics characterastic of two kinds of locomotive bogies,then influence that the impact have on the traction pins.Take a certain type of meter gauge locomotive for instance. Use dynamics software of SIMPACK to establish a vehicle and track coupling dynamics model ,combine with the characteristics of foreign mountain lines.Simulate the actual working conditions. Due to the existence of freedom of traction vertical clearance, The traction pin subject to greater longitudinal impact while running on the poor line in high speed. According to the original program the maximum longitudinal forces of three traction pins are 165kN, 197kN and 167kN. For upswing plan the figures are 165kN, 141kN and 186kN. The Traction pins and horizontal stopper occurs violent collision in mall radius curve condition according to the original program. The second traction pins suffered the biggest lateral impact reach 259kN. While considering the wheel wear, the impact even reached 785kN.As improved method ，the traction pins lateral impact is small, no more than 45kN.The results showed that:the large lateral force generated between traction pins and lateral stop may cause bolts’ looseness and fracture while crossing the small radius curves, On the poor line, longitudinal impact caused by track irregularity may also result in the problem.