Abstract: Calculation model for activities of the components in CaOAl2O3 and CaOSiO2Al2O3 slags was established according to the molecule and ion coexistence theory. The activities of the components in CaOAl2O3 and CaOSiO2Al2O3 slags were calculated， and the influence of w(CaO) on the activities of the components was discussed. The results show that when the w(CaO)in CaOAl2O3 slag is less than 45%， with increasing the w(CaO)， the activities of 3CaO·Al2O3 and 12CaO·7Al2O3 in slag increase， however， the activity of CaO·Al2O3 changes little. When the w(CaO)in CaOAl2O3 slag is more than 45%， with increasing the w(CaO)， the activities of CaO·Al2O3 and 12CaO·7Al2O3 in slag decrease， however， the activity of 3CaO·Al2O3 increases slightly. In the CaOSiO2Al2O3 slag， the activity of 12CaO·7Al2O3 is lower than that in the CaOAl2O3 slag， with increasing the w(CaO)， the activities of CaO and 3CaO·Al2O3 increase， and the activity of 2CaO·SiO2 decreases， however， the activity of CaO·Al2O3 increases at first and then decreases.

Key words: slag, activity, coexistence theory, 12CaO·7Al2O3, 3CaO·Al2O3, 2CaO·SiO2