Abstract: Shifting-yoke of a gear-box for a wheeled chariot is investigated to make out the causes of fracture failure in the process of use.From the angle of materials,the failure is found to be caused by fatigue damage.By calculating with a shifting design load of 1?350?N with non-liner finite element software MSC Marc and fatigue life software MSC Fatigue,the strength and life of the shifting-yoke can meet the design requirements.Stress and life are calculated under a wide range of loads.Following Miner's accumulated damage theory and time of use of the shifting-yoke,the practical shifting load should be between 1?400～1?800?N,which is beyond the design load,will result in damage accumulation and fatigue fracture.