Abstract: A polycarboxylate-based water reducer was synthesized with methyl allyl alcohol polyoxyethylene ether and acrylic acid as main raw materials by controlling pH of polyether monomer solution (base material). The pH range of polyether macromonomer solution and the effect of different acid types on the performances of water reducer were determined by measuring the conversion of polyether, the water reducer's relative molecular weight and molecular weight distribution index, and evaluating the application performances of water reducer. The results showed that the conversion rate of polyether monomer was increased by controlling the pH of the base material. When the pH was controlled at 3, the conversion rate of polyether was the highest, which increased from 87.41% of the blank to 95.43%. Moreover, the molecular weight distribution index of synthetic water reducer was the lowest, decreasing from 3.183 to 2.884. When sulfuric acid was used to control the pH of the base material, sodium sulfate was present in the solution, its rapid dissolution reduced the encapsulation and consumption of polycarboxylate superplasticizer by cement hydration products, which was more conducive to improving the dispersibility of polycarboxylate superplasticizer. The results revealed that the overall performance of polycarboxylate superplasticizer can be improved by controlling the pH of polyether macromonomer solution without changing the synthetic process of water reducer.