Phase forming reactions of C2S, C4A3 and C4AF which are major mineral of modified belite cement were investigted by adding calcium phosphate and barriete, It has been found that calcium phosphate stabilizes $eta$-C2S phase while have negative effects on formation of C4AF. Barrite loweres the forming temperature of C2S and accelerates the formation of C4AF. Both additives retard the formation of C4A3 and lower the burnabi-lity of MBC clinker. It also has been found that P2O5 and SO3 are well-incorporated in C2S and BaO is well-incorporated in C4A3