The invention relates to a preparation method of polycarboxylic acid concrete dispersers, comprising the following steps: (1) free radical copolymerization is carried out: a monomer A and a monomer C carry out free radical copolymerization under a condition that a monomer B is used as solvent according to mole ratio of 1.01 : 1 to 1.5 : 1, wherein the monomer A is (alkyl) vinyl alkyl acid ester, the monomer B is mono-alkoxy poly alkylene glycol ether, and the monomer C is maleic anhydride; the mole ratio of the monomer B and the monomer C is 0.1 : 1 to 1 : 1; (2) esterification grafting reaction is carried out: the polymer prepared by the step 1 is warmed up and esterified, so as to graft monomer B on a acid anhydride group led in by the monomer C; (3) after the esterification reaction isfinished, reaction product is added with water for dilution, and alkalinity substances are added in for adjusting the pH value to 6.0 to 8.0. Organic solvent with toxic substances is not used, thereby effectively avoiding volatile organic solvents from damaging the environment and human body; in addition, the production cost is low, the process is simple and the production efficiency is high.