This paper mainly deals with the changes of external morphology, the activity of peroxidase and nit rate reductase, the content of chlorophyll, O₂^-· and MDA in Brasenia schreberi by Cr⁶⁺ treatment.The results show ed the reason of Cr⁶⁺ injuring Brasenia schreberi w as that Cr⁶⁺ inhibited the activity of enzymes and damaged membrane.In the third day, the content of chlorophyll reduced with the increasing concent ration of Cr⁶⁺, the activity of peroxidase was the highest at 10 mg/L, the activity of nit rate reductase was a lit tle higher at 5mg/L, but reduced with the increasing concent ration of Cr⁶⁺ up to 40mg/L, the content of O₂^-· w as the highest at 5mg/L, and a little higher than control group at 10mg/L, then it reduced with the increasing culture concentration of Cr⁶⁺, the trend of changes in MDA was relatively similar with that of O₂^-·.