Hydration of granulated blastfurnace slag-gypsum-$C_4A_3ar{S}$ clinker/modified converter slag clinker was investigated to develop the cement of slag-gypsum system. In the hydration of granulated slag-gypsum-$C_4A_3ar{S}$ system clinker, the hydrates such as ettringite, CSH gel and $AH_3$ gel were formed, and the strength of hardened body would be increased by forming compact microstructure. The modified converter slag clinker which contains alite and calcium aluminate was synthesized, and the hydration reactivity of the cement from this clinker, gypsum and granulated slag is similar to usual portland cement, and the hydrates were mainly CSH, ettringite, and $Ca(OH)_2$