Influences of polycarboxylate superplasticizer （PCA）, polynaphthalene sulphonate superplasticizer （PNS） and aliphatic superplasticizer （SAF） on early hydration of C3A were investigated by X ray diffraction （XRD）, total organic carbon （TOC） measurement and chemical analysis. Experimental results indicate that the adsorptions of three kinds of superplasticizers on C3A are different. Organo mineral phases （OMP） are formed in all three kinds of hydration systems, and the intensity and width of characteristic diffraction of OMP for PNS system are higher than those for PCA and SAF systems. PCA and PNS accelerate the hydration process of C3A, however, SAF inhibits the dissolution precipitation process of C3A at early age. Effect of PNS on the formation of calcium sulphoaluminate is less than that of PCA and SAF, while PCA and SAF can accelerate the formation of calcium monosulphoaluminate at initial hydration stage. The study of effects of superplasticizers on early hydration of C3A reveals the essence of compatibility between superplasticizers and cement.