Abstract: Vitrification is considered as a promising technology for Hazardous Waste Incineration Ash and Slag(HWIAS), which can realize the reduction, innocent treatment and resource utilization of HWIAS. The main oxide components of HWIAS are CaO, Al₂O₃, SiO₂, Na₂O, FeO_x and MgO, and the thermodynamic properties and equilibrium phase relations of the CaO-SiO₂-Al₂O₃-Na₂O-FeO_x-MgO system are essential data for the slag formation in thermal processing of HWIAS. According to the main components of HWIAS, the equilibrium phase relations and liquid phase characteristics of the multicomponent systems were calculated for different temperature and oxygen partial pressures by using the thermodynamic software FactSage. The multicomponent systems include CaO-SiO₂-Al₂O₃-Na₂O, CaO-SiO₂-Al₂O₃-FeO_x, CaO-SiO₂-Al₂O₃-Na₂O-FeO_x and CaO-SiO₂-Al₂O₃-Na₂O-FeO_x-MgO systems. The results showed that the effects of temperature and oxygen partial pressure on the equilibrium phase relations and liquidus characteristics of the four multicomponent systems mentioned above were remarkable. The liquid zone enlarged with increasing temperature from 1 400 to 1 500 ℃. For the multicomponent systems containing FeO_x, the liquid zone increased with the reduction of oxygen partial pressure. In addition, the equilibrium phase relations and liquidus characteristics of different multicomponent systems differ greatly at the same temperature and oxygen partial pressure, so the reasonable technological conditions should be chosen according to the thermodynamic properties of the actual oxide system in HWIAS.