Two kinds of Gemini quaternary ammonium salts were synthesized by using triethylamine and 1,4-p-dichlorobenzyl as the linking group and N,N-Dimethylethanolamine (or triethylamine ) as the head group (labeled as KNJ-1 and KNJ-2).which was compounded with polycarboxylate superplasticizers to improve the negative effect of the clay on the polycarboxylate superplasticizers, the effect of the terminal hydroxyl group on the clay effect was investigated. The structure was characterized by FT-IR and 1H NMR.The effect of anti-clay agent was evaluated by the fluidity of cement paste. The mechanism was reveled by X-ray photoelectron spectroscopy,X-ray diffraction and Zeta potential measurement. The re-sults show that the addition of KNJ-2 increased the initial fluidity by 25 mm, and the fluidity increased by 165 mm after 2 hours, showing a good anti-clay advantage. XRD and XPS results showed that KNJ-2 is superior to KNJ-1 in surface and interlayer adsorption of montmorillonite. And the Zeta potential of montmorillonite was increased from the initial -15.67mV to -0.15mV.This is ascribed to hydroxyl group which can generate hydrogen bond with the surface and interlayer of the montmorillonite, occupying a large number of active sites. polycarboxylate superplasticizers can be prevented from being absorbed in surface and interlayers of clay to ensure better dispersion performance ,presenting a marked anti-mud ef-fect.