A fluorescent probe (ED) was designed and synthesized using caffeic acid to detect N2H4 rapidly. Its structure was characterized by 1H NMR, 13C NMR, and HRMS. It was found that the probe ED had high selection and high sensitivity recognition of N2H4 by fluorescence spectroscopy, and the detection limit during the detection process was 0.31 μmol/L, the optimal pH value range was 3~8, and the response time was 48 s. MS and 1H NMR proved that the unsaturated ketone in the probe structure reacted with N2H4 to form pyrazole ring in the fluorescence response of probe to N2H4. In addition, after the probe ED interacts with N2H4, the color of the solution changes from colorless to yellow, which can realize the "naked eye detection" of N2H4. Probe ED was successfully used for the detection of N2H4 in actual water samples.