Abstract: Primary steel spring is important bearing and damping component of EMU, the faults of which occur mainly as fracture and wear. At present, most analysis of steel spring fracture faults is based on simulation and material analysis methods, and the root cause of the abnormal stress is not studied in depth. From the perspective of vibration response, the fatigue fracture problem of primary steel spring in certain EMU is analyzed in depth. The physical\|chemical analysis, vibration mode test and wheel state investigation are comprehensively adopted to locate the root cause of spring failure, that polygon exists in wheel and the induced forced vibration leads to contact fatigue fracture of primary steel spring. Through wheel lathing, the problem of steel spring fracture is solved.