Abstract: The pockmarks in the raceway of coupling bearing for X-Ray tube were found during the process of assembly inspection, the formation causes of pockmarks were analyzed by means of macro analysis, chemical composition analysis, hardness test, metallographic examination and so on. The results show that the cooling rate of the raw material was slower in casting process, and large bulk angular carbides were produced. In the process of raceway grinding and ultra fine grinding, large bulk angular carbides were peeled off, which resulted in pockmarks on the bearing raceway.