A series of polycarboxylate superplasticizers(PCEs) with different carboxylic density have been synthesized through radical copolymerization in aqueous phase. The dispersing capability and the adsorption behavior of the PCEs were analyzed via flow table test and ultraviolet spectrophotometer. The influence of different molecular structured PCEs on the hydration properties of cement paste was studied through isothermal conductive calorimeter and the X ray diffracmeter (XRD). The results show that higher carboxylic density in PCE molecules leads to greater adsorption amount onto cement surface and a higher dispersing capability in fresh cement paste. Increase in carboxylic density results in enhancement in cement hydration process, which is due to increase in the formation of Ca(OH)2 product, increase in the maximum hydration evolution rate in acceleration period, and increase in the acceleration rate of hydration rate in the early stage of the acceleration period.