The invention discloses polymer nanoparticles capable of detecting hypochlorous acid and copper ions. The polymer nanoparticles are novel polymer nanoparticles prepared by taking a polyethylene glycol monomethyl ether chain transfer agent, styrene, 2-aminoethylmethacrylate hydrochloride, rhodamine B isothiocyanate and a 9,9-dioctyl polyfluorene-benzothiadiazole alternate copolymer as raw materials. The polymer nanoparticles can realize high-sensitivity ratio fluorescence detection on the hypochlorous acid and the copper ions in a pure water solution. Compared with an existing fluorescence detection technology, the prepared polymer nanoparticles have a double-ratio detection function and good biocompatibility; a synthetic route is simple and a detection method is simple and convenient; the polymer nanoparticles are applicable to amplified synthesis and actual production application, and have a great application prospect in the technical fields including analytical chemistry, life science, environmental science and the like.