The invention provides a hypochlorous acid fluorescent probe with quick response and high selectivity and sensitivity by molecular structure design, as well as a preparation method thereof and application of the hypochlorous acid fluorescent probe to detection of hypochlorous acid in an aqueous solution and a cell. The fluorescent probe can be applied to detection of the hypochlorous acid in the aqueous solution or a biological system, and detection comprises fluorescence detection, cell imaging and visual colorimetry. The fluorescence intensity forms linear positive correlation with the concentration of the hypochlorous acid within a certain concentration range, and the concentration of the hypochlorous acid can be quantitatively measured. The hypochlorous acid fluorescent probe is easy to synthesize, and a posttreatment process is relatively simple; selective and rapid detection of the hypochlorous acid molecular probe is realized, the selectivity is good, and the hypochlorite fluorescent probe is high in resistance to interference of other molecules, is a simple, rapid and sensitive hypochlorous acid molecular specific detection reagent, and has broad application prospect in the field of biomolecular detection.