Abstract: The total oxygen,the contents of[H] and[Al],the inclusions and the compositions of slag by RH and VD refining treatment are compared under the other same conditions. The results show that dehydrogenation by RH is better than VD,while deoxidation by VD is better than RH. The final content of[Al] and the basicity of slag processed by VD increase and the compositions of inclusions deviate from the plastic zone. The content of Mg O in slag processed by RH increases obviously and the compositions of inclusions are dispersed. While the content of Mg O in slag processed by VD changes slightly and the compositions of inclusions are concentrated. The differences are ascribed to refractory shedding in the snorkel of RH unit which leads to the increase of external inclusions. The suggestions for vacuum refining are as follows:the quality of refractory should be improved and the gunning for snorkel should be reduced with the processing by RH. While the amount of lime and the basicity of slag should be decreased,and the treatment time should be increased with the processing by VD.