Abstract: It is studied of the effect of deltamethrin on aquatic organisms in a rice field-fish pond ecosystem, simulation that rainfall event began two hours after deltamethrin was applied to the rice field, and field water was all drained into the pond. Experimental results showed that: No death wad found of fish or oyster in the entire experimental period, and the measured results of residue and toxicity was correspond to that of harmness. A large of experimental shrimp around the drainage point died. The experimental shrimp of other area only had less effect and on death was found. Shrimp had a obvious avoidibility to deltamethrin, the harmness degree of deltamethrin on shrimp mat be lower in natural water than that of the netted in the experiment. The zooplanktons in the fish pond were seriously harmed after the field water was drained into the pond, but zooplanktons may returned to normal two weeks later. The experimental results showed that deltamethrin had no harmful effect to fish breeding in rice field.