Hardness is an important indicator of rolling bearings. It is closely related to the fatigue strength, wear resistance and elastic limit of the material, which directly affects the life of the rolling bearing. The hardness of the bearing usually depends on the way and size of the bearing under load, the bearing size and the overall thickness of the bearing. Rolling bearing steel hardness to be appropriate, too large or too small will affect the bearing life. As we all know, the main failure of rolling bearing contact fatigue damage, and due to poor wear resistance or dimensional instability and the loss of bearing accuracy; bearing parts if the lack of a certain toughness, under greater impact load will be due to the occurrence of brittle fracture Bearing damage. Therefore, we must be based on the specific circumstances of the bearing and the way to determine the destruction of the bearing hardness. Bearing due to fatigue spalling or poor wear resistance to the loss of the case, the bearing parts should be used higher hardness; bearing greater impact load bearing (such as rolling mill: bearings, railway bearings and some automotive bearings, etc.) should be appropriately reduced Hardness to improve bearing toughness is very necessary.