The effect of single mineral clay on the fluidity of cement paste with adding polycarboxylate superplasticizer（PCs） was studied.Water clay ratio and absorption quantity to PCs of four kinds of single mineral clay(Ca montmorillonite(MMT),Na MMT, Illite, Kao lin)were measured. Basing on the extra addition of water and PCs, study of the effect of single minerals clay on the dispersibility of PCs was proceeded. The results demonstrate that the extra addition of water and PCs can mainly remove the effect of Illite and Kao lin to the fluidity of cement paste, but the effect of MMT still exists significantly. The single mineral clay（absorbed polycarboxylate superplasticizer） was analyzed by using infra red spectroscopy（IR） and XRD small angle diffraction. The results indicate that PCs is absorbed into the interlayer of MMT, which is the main reason that the absorption quantity of MMT to PCs and the effect on the dispersibility of PCs is lager than other kinds of single mineral clay.