Abstract: The causes of the grinding cracking of an inner-ring cam were analyzed by means of chemical composition analysis, metallographic examination and hardness test. The results show that the quenching temperature of the inner-ring cam was high and the tempering was insufficient, which resulted in the coarse acicular martensite microstructure and more retained austenite, and increased the sensitivity of grinding cracking and residual internal stress of the inner-ring cam. At the same time, the grinding feed amount was large and the cooling was inadequate, so the grinding affected layer and large grinding stress generated on the surface of the inner-ring cam. The combination of grinding stress, residual stress and rolling stress of the high speed grinding resulted in the grinding cracking of the inner-ring cam.