Abstract: The crack on crankshaft of automobile engine was analyzed by macroscopic observation,metallographic inspection and hardness testing methods.The results show that the tiny crack on the transition plane of crankshaft journal to crank arm had the characteristic of the grinding crack.The tiny crack was the typical grinding crack.The formation of grinding crack was mainly caused by grinding heat due to unreasonable grinding process.Reducing the grinding heat was the key to eliminate the grinding crack.