The invention relates to a method for detecting a water body sterilization byproduct. The method comprises the following steps: S1, modifying a Mn-doped ZnS quantum dot with sulfur-containing amino acid, and performing activation treatment on the modified quantum dot; S2, mixing an amino acid solution with the quantum dot solution activated in the step S1, stirring to couple the two components, performing centrifugal separation, washing, precipitating, and drying so as to obtain amino acid modified quantum dot for later use; S3, mixing a water sample to be tested with the amino acid modified quantum dot solution obtained in the step S2, oscillating to enable the components to react, and measuring the fluorescence intensity of the solution by using a molecular fluorophotometer. By adoptingthe method, on the basis of excellent florescence properties of quantum dots, the Mn-doped ZnS quantum dot is modified with a specific amino acid for a first time, and by virtue of a charge migrationreaction of the amino acid with a target, namely benzoquinone, fluorescence quenching of the quantum dot is resulted, and a rapid and sensitive fluorescence detection method for water body sterilization byproducts is established.