Abstract: Traditionally,the eco-toxicological test system had only concern about effects of exotic chemical on single species,so that the test results deviated from real responses to natural ecosystem.Also the complexity and recoverability of natural ecosystem made it difficult to obtain clear conclusion of field experiment.Undoubtedly the microcosm test was a good route to get rid of these dilemmas.The effects on ecosystem of atrazine were determined by biotoxicity test on single species and standardized aquatic microcosm test.It can be concluded from the results that atrazine impacted the growth of algae at level of 0.023 mg/L.Also it influenced the growth of algae and the living of shrimps at level of 0.033 mg/L,but no significant toxic effects on other zooplankton such as Daphnia magma,ostracods,rotifers and so on was detected.The safety threshold value of atrazine in aquatic ecosystem was 0.009 mg/L,high toxic for photosynthetic organisms,but slightly toxic or took an indirect effect for zooplankton.