Abstract: For bearing steel in the cold and hot charging heating for laboratory thermal simulation, analyzed the level of casting billet grain size of hot charging by different heating temperature, and compared the grain size under the condition of cold charging, find the reasonable hot charging heating temperature. The results show that： when the hot charging temperature over 700℃, compared with cold charging, its casting billet organization of grain become bulky, grain size level between grade 1 ~ 2； According to the work site ,the before phase change cooling rate of casting billet as an average of 0.41 ℃/s, the hot charging temperature of GCrl5 bearing steel casting billet should be controlled less than 670 ℃.