Phenylalanine was grafted onto the end of maleic anhydride polyethylene glycol ester to synthesize amino acid modified unsaturated acid ester， which was introduced into polycarboxylate superplasticizers （PCE） to prepare clay resistant PCE. The effects of the amount of amino acid modified unsaturated acid esters， initiator and chain transfer agent on clay resistance of cement-montmorillonite slurry were discussed. Combined with the changes of the adsorption capacity， layer spacing and pore structure of montmorillonite， the effect mechanism of clay resistant PCE was studied. The results show that compared with ordinary PCE， the initial fluidity of cement-montmorillonite slurry prepared by clay resistant PCE increases by 18.6% and the spread flows loss rate decreased from 39.5% to 13.7%. Amino acid modified unsaturated acid ester reduces the adsorption of PCE on montmorillonite and inhibits the intercalation adsorption and surface adsorption of montmorillonite.