Abstract: The photochemical degradation characteristics of chlorfenapyr and its influencing factors were investigated in different solvents under high-pressure mercury lamp (HPML).Under simulated experiment in laboratory,the half-life of chlorfenapyr in pure water was 25.86 min at 2 mg/L,the photolytic rate negatively correlated with the increasing concentration of chlorfenapyr in pure water at a range from 1 mg/L to 10 mg/L.The photolysis half-lives of chlorfenapyr were 42.52,24.49 and 32.39 min in buffer solution of pH 5,7 and 9,respectively.The result indicated that the degradation velocity of chlorfenapyr was the fastest in the buffer solution of pH 7.The photochemical degradations of chlorfenapyr were inhibited in water solutions that contained NO2-,NO3- or NH4+.The inhibition of NO2- and NO3- were stronger at the concentrations less than 20 mg/L,the inhibition of NH4+ was stronger at the concentration greater than or equal to 20 mg/L.The photolytic rates of chlorfenapyr in different organic solvents showed the following sequence:n-hexane>methanol>ethyl acetate>acetone.The photodegradation rate had no correlation with organic solvent polarity.The results provided a scientific basic for environmental risk assessment of chlorfenapyr.