Abstract: Based on the industrial experiments of VD treatment at HZSteel, the effect of slag on[Al]s 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 the[Al]s 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.