Abstract: To study the effect of metal icon Cr、Co、Pb on SOD、POD、MDA in Lemna minor, we culture Lemna minor in Aqua NO.104 nitrogenous medium by adding metal icon Cr、Co、Pb in different concentration course, respectively. After six days cultivation, we detect the change of the SOD、POD、MDA content. The results showed that under the single stress the SOD、POD、MDA can vary regularly. The Lemna minor can effectively resist the damage of these metal icons through theire own defense system in very low concentration, however, when the Cr6+、Co2+、Pb2+ concentration is more than 1.5mmol/L、0.8mmol/L、0.5mmol/L, Lemna minor cannot repair the damage caused by it.