Abstract: It is well known that the unbalance between production and elimination of the active oxygen often caused by manychemicals and the antioxidant systems play an important role in the resistance to the stress. Heavy metal is a major pollutant inwater body,but little work has been done on the response of antioxidant enzyme activity in aquatic plants to heavy metals. In orderto investigate the molecular toxicological effects of heavy metals on antioxidant enzyme activity in higher hydrophytes, Hydrillaverticillata(L. f.) Royle,a wide spread submerged macrophyte in China is selected and cultivated in nutrient solution containingdifferent concentration of Cd,Cu,Zn for 7days. The results showed that three heavy metals accelerated the generation rate of tocertain extent ;Cu inhibited the SOD,POD and CAT activity ;Cd decreased the SOD and POD activity,while CAT activity in creased under 5mg/L ;Zn had a similar influence with Cu and Cd on SOD,but both POD and CAT activity were enhanced by015-5mg/L concentration. Evaluation with the method of grey relational grade analysis suggested that POD, POD and CATplayed an important role in protection against the injury resulting from active oxygen under Cu,Cd and Zn stresses,respectively.SOD was the most susceptible to the adversity. Chlorophyll content decreased when treated with Cd and Cu,and augmented whenZn concentration was 015-5mg/L. Chlorophyll a/b value was higher than that of the control under all Zn concentration ;015mg/L Cu and 015-1mg/L Cd treatment. The soluble protein content ascended when treated with 015-5mg/L Zn and 015-1mg/LCd,but descended by all Cu treatment. In general,the toxicity of Cu was the most serious following by Cd and Zn. The lethal concentration was 015-1mg/L for Cu |1-2mg/L for Cd and 5-6mg/L for Zn. Therefore, SOD activity served as a sensitivebiomarker to evaluate the toxic effect of heavy metal on submerged macrophytes and H. verticillata was impressible to the Cu pollution in water environment.