Abstract: Based on the industrial experiments of VD treatment at HZSteel, the effect of slag onAls was studied as well as the effects of vacuum holding time and vacuum degree on the total oxygen content. The results show that the higher the basicity, the less theAls reduction in the steel in the basicity range of 2.5~4.5, while the reduction trend of CaO is increased;The longer the vacuum processing, the lower the total oxygen content in the steel, but not obviously decreases after 16 min;When vacuum is more than 67 Pa, the total oxygen content in steel drops with the decrease of the vacuum;However, when vacuum is less than 67 Pa, the total oxygen content in steel rises instead of decreases.