The invention relates to the technical field of concrete admixtures and discloses a water reducer capable of improving performance of concrete. The water reducer is prepared from components in parts by weight as follows: 310-400 parts of methyl allyl polyethenoxy ether, 25-30 parts of acrylic acid, 5-8 parts of an oxidizing agent, 12-16 parts of inorganic base, 0.1-0.6 parts of organic acid and 2.0-2.8 parts of inorganic ammonium salt. The organic acid comprises mercaptoacetic acid, and the inorganic ammonium salt comprises ammonium persulfate. The water reducer prepared in proportion has good adaptability to cement and has the technical effects of delayed coagulation, plasticity maintaining and the like. The water reducer prepared in the proportion has high water-reducing rate and low shrinkage ratio, can improve the waterproof and anti-seepage capacity of the concrete and greatly reduces self-contraction of concrete in the later stage. Adverse factors such as an alkali-aggregate reaction, corrosion of steel bars and the like caused by traditional admixtures and the like can be reduced due to low chloride and low alkali. The water reducer has extremely high affinity and dispersing capacity for cement, fly ash, mineral powder and the like, reduces surface tension of a pore solution and enables the generated concrete to be compact in structure.