Abstract: Cracks were found on the surface of a roller wheel with material of 20CrMnMo steel when grinding after carburizing and quenching.Means such as macro examination,chemical compositions analysis,non-metallic inclusions examination and metallographic examination were used to analyze the formation causes of the surface cracks.The results show that the surface cracks of the roller wheel were grinding cracks,and unevenness sand grain on the edge of the grinding wheel and unreasonable grinding process were main reasons for the grinding cracks.The problem of roller wheel producing grinding cracks was well solved by improving the grinding process.