The invention relates to a chemical cleaning method for reducing a collective dose of an in-service pressurized water reactor nuclear power plant. The method comprises the following steps: connecting a mobile decontamination device; performing oxidation treatment for 6-8 hours; performing reduction treatment with a reducing solution having a pH value of 2-2.5 for 3-5 hours, wherein the reducing solution comprises 0.2-0.65 g/L nitric acid, 0.4-0.7 g/L L-ascorbic acid and 0.2-0.7 g/L an auxiliary compound; judging whether to repeatedly perform oxidation and reduction; performing rinsing treatment with an alkalinizing solution for 2-4 hours; and performing circulating flushing. According to the invention, the chemical cleaning method is suitable for in-situ decontamination of a primary loop of the in-service pressurized water reactor nuclear power plant and an internal surface of nuclear auxiliary system equipment; the dose rate of a to-be-decontaminated regional environment is reduced to 1/2-1/10 of the original dose rate within a short time (usually 1-3 days); and no adverse effect is made on the rerun of a set.