Abstract: In order to assess the deratization effect of bleaching powder on Eurytemora affinis in different developmental stages under natural attenuation situation,a toxicity test of bleaching powder on Eurytemora affinis in water bodies with different fertility at 5℃ and 25℃ was carried out.The results showed that water fertility and temperature were the attenuation influencing factors of bleaching powder;the tolerated concentration to bleaching powder(available chlorine)of eggs(32.000 mg/L),adults(3.200 mg/L),copepods(1.000~3.200 mg/L)and nauplii(1.000 mg/L)of Eurytemora affinis exhibited a decreasing trend in turn.These results indicate that when bleaching powder is used to kill Eurytemora affinis,its dosage should be determined with the consideration of different developmental stages of Eurytemora affinis,water fertility and temperature.