Through fluidity of cement paste the improvement of dispersion property of polycarboxylate superplasticizer(PCE) after adding montmorillonite by anti clay agent(JJA KNJ) can be evaluated, and its mechanism can be elucidated by TOC, TG, XRD and SEM. The results show that anti clay agents(JJA KNJ) can improve the dispersion of PCE after adding montmorillonite and significantly increase the dispersion of PCE with time and enhance the slump retention performance. When JJA KNJ and PCE coexist in the synthetic cement pore solution, JJA KNJ decreases with the adsorption of PCE on montmorillonite. Montmorillonite surface becomes smoother and forms smaller pores after anti clay agents JJA KNJ; cationic polar terminal of JJA KNJ dissolves in water and adsorbes on the surface of the montmorillonite particles, thus forming a layer of organic cationic polymer protective film to prevent the side chain of PCE onto montmorillonite interlayer. JJA KNJ has a significant stabilizing effect under alkaline conditions of hydration of cement, stabilizing effect will not be significant attenuation with the extension of time.