The chemical composition and form of impurities in titanium gypsum and their effects on properties of cement were introduced when used as set retarder for Portland cement. Experimental results show that the impurities are mainly Fe (OH)_3, FeSO_4 and Al(OH)_3, and they may do little effect to Portland cement. The properties of cement with titanium gypsum are similar to those of Portland cement with natural gypsum,