Based on the fact that the ZnO nanoparticles (ZnO NPs) can enhance the weak chemilu-minescence (CL) of the luminol-H₂O₂ system, a simple, fast and sensitive flow injection CL method was developed for the determination of H₂O₂ in rainwater. Experimental parameters affecting CL were optimized, including pH and concentrations of ZnO NPs, luminol and H₂O₂. Under optimal conditions, the logarithm of CL peak area (lg A) is linear with the logarithm of the concentration (lg c) of H₂O₂ when the concentration of H₂O₂ ranges from 0.06 to 20 μmol/L and its limit of detection is 0.016 μmol/L(3σ). The method has been successfully applied to the determination of H₂O₂ in rainwater, giving recovery rate in the range of 95%~102% and RSD (n=11) of 2.41%.