Abstract: On the basis of the ladle's thermal circulation, a heat transfer mathematical model of melt steel was established, and was applied to the respective metallurgical unit in RH-CAS. OB combined process at Wuhan Iron and Steel Company. The main influential factors of the melt steel temperature in the CAS-OB process was analyzed. The temperature system in the RH-CAS.OB process was calculated and optimized on the basis of the new computer model. And the results provide the theoretical instructions to practice production.