Abstract: A method for the determination of trace of 3-hydroxypropanal (3-HPA) in water by high performance liquid chromatography combined with fluorescence detector after derivatization with dansulfonyl hydrazine was proposed. The water sample (1.0 g) was mixed with 2.0 mL of acetonitrile solution containing 200 mg·L^-1 dansulfonyl hydrazine and 1.0 mL 3.0% (volume fraction) acetic acid solution, and its volume was made up to 50 mL with acetonitrile. Then the mixed solution was derived at 40 ℃ for 30 min. Agilent Eclipse Plus C₁₈ column was used as the stationary phase, and gradient elution was performed with the mixtures of acetonitrile and 0.10% (mass fraction) perfluorobutanoic acid solution at different volume ratios as the mobile phase, with fluorescence detector for determination. It was shown that derivatization reagent dansulfonyl hydrazine and 3-HPA derivative could be separated at baseline within 20 min, and linear relationship between the mass concentration of 3-HPA and the peak area of derivative was kept in the range of 7.6-380.0 μg·L^-1, with detection limit (3S/N) of 1.1 μg·L^-1. The method was applied to analysis of actual samples, with RSD (n=6) of the determined values was 0.71%, and the spiked recoveries of 3-HPA were in the range of 98.0%-102%.