The invention discloses a method for wet maintenance of a nuclear power plant steam generator by a nuclear-grade polyacrylic acid dispersing agent. The method comprises the following steps: (S1) preparation of a nuclear-grade dispersing agent: the nuclear-grade dispersing agent contains polyacrylic acid, non-polymerized acrylic monomers, isopropanol and the balance of demineralized water; (S2) preparation of an auxiliary reagent: ammonia water and hydrazine are uniformly mixed in a chemical reagent charging tank of a nuclear power plant; (S3) preparation of the demineralized water: the demineralized water is fully injected in an auxiliary water feeding tank of the nuclear power plant; (S4) maintenance: the nuclear-grade dispersing agent in the step (S1), the auxiliary reagent in the step (S2) and the demineralized water in the step (S3) are synchronously pumped into a water feeding master pipe of a steam generator; and (S5) maintenance effect estimation: if the dry weight of filter slag, the total iron in maintenance liquid and the average concentration of hard substances are higher than conventional maintenance levels, the maintenance effect of the nuclear-grade dispersing agent is better than the conventional maintenance. The method can totally reduce the scaling level of the steam generator, improves the heat transfer, relieves the scaling corrosion of a heat transfer pipe,and has the advantages of obvious benefit and low investment.