In order to remove or reduce the negative effect of MgO in calcium aluminate slags, the method of adding Na 2O into calcium aluminate slags was studied and its effect on leaching mechanism was also analyzed. The results show that the alumina leaching efficiency of the calcium aluminate slag increases from 68.73% to 80.86% with Na 2O content increasing from 0 to 4% when MgO content is 3%. The XRD results show that the quaternary compound C 20A 13M 3S 3 disappears when Na 2O content increases to 4%. The addition of Na 2O cannot remove the negative effect of MgO on leachability completely. XRD and EDS results indicate that Na 2O can come into the lattice of 12CaO·7Al 2O 3 and promote the formation of 12CaO·7Al 2O 3