Abstract: Provided are a polymer medicament for treating hyperkalemia, and a preparation method thereof. Specifically, a polymer is provided, and the polymer includes repeating units obtained by polymerizing a monomer and a crosslinking agent. A molar ratio of the monomer to the crosslinking reagent ranges from 1:0.02 to 1:0.20. The monomer includes an acidic group and a pKa-reducing group next to the acidic group. The acidic group is selected from the group consisting of sulfonic acid group (—SO3—), sulfuric acid group (—OSO3—), carboxylic group (—CO2—), phosphonic acid group (—OPO32—), phosphate group (—OPO32—), and sulfamic acid group (—NHSO3—). The pKa-reducing group is selected from the group consisting of nitro, cyano, carbonyl, trifluoromethyl, and halogen atoms. The crosslinking agent has three or four reaction sites. The polymer can be used to treat hyperkalemia.