The aim of this paper is to find out regularity of comb-type water reducers effect on early hydration of cement and to guide engineering applications of comb-type water reducers. Microstructures of early hydrates of cement superplasticized by three typical polycarboxylates were observed by SEM, and the electronic characteristic data of cement hydrates were analyzed. It is found that comb-type water reducers can accelerate hydration rate of cement minerals. Moreover, acrylic acid based copolymer promotes formation of ettringite, and maleic anhydrite based copolymer speeds up formation of monosulfoaluminate. Therefore, early hydration of cement and engineering properties of concrete are dominated by the kind of comb-type water reducers. Suitable choice should be made according to application requirements of concrete engineering, and modification should be done by blending retarders, air entraining agent or defoaming agent if needed.