The invention discloses a preparation method for carboxylated polystyrene microspheres. The method comprises the following steps: 1) mixing monomer styrene, solvent ethanol, initiator 2,2'-azobisisovaleronitrile, dispersant polyvinylpyrrolidone and surfactant triton, and performing a reaction under the conditions of a nitrogen gas atmosphere, a rotation speed of 200 r/min and temperature of 70 DEGC; 2) uniformly mixing an equal amount of monomer styrene, solvent ethanol and an acid functional monomer acrylic acid, adding the mixed material into the reaction system in the step 1), and continuing a reaction; and 3) after the reaction is completed, stirring the reactant in ethanol, performing dispersion, performing centrifugation, and performing washing to obtain the carboxylated polystyrenemicrospheres. The method disclosed by the invention divides the reaction into two parts, so that the reaction is more sufficient, the monomer conversion rate is greatly improved, and the prepared polystyrene microspheres are uniform, and have a large particle size, wherein the particle size can reach a micrometer size.