Abstract: An experiment of hydroponic culture was carried out to investigate the effects of copper and chromium on Lythrum salicaria Linnaeus aseptic seedlings. The plants were cultured in 1/10 sterile Hoagland nutrition liquid with Cu²⁺ at 0, 5, 10, 20, 40 mg/L and Cr⁶⁺ at 0, 5, 10, 20, 40 mg/L respectively for 4 days. We analyzed the toxic effects on chlorophyll content, malondialdehyde (MDA) content, the activity of antioxidant enzymes (SOD, POD, CAT), soluble sugar content and soluble protein content of the seedlings. The results suggested that the osmotic regulatory substances (soluble sugar and soluble protein) increased at low copper concentrations and then decreased at higher concentrations. With the increase of Cu²⁺ concentration, the degree of membrane peroxidation increased, while the chlorophyll content was not significantly affected. The activity of antioxidant enzymes (SOD, POD and CAT) was high under the copper treatment. With the increase of chromium concentration, the chlorophyll content was also not inhibited. The extent of membrane peroxidation was not significantly affected when the chromium concentration was 0—20 mg/L. The CAT activity was continuously inhibited, but SOD and POD were well activated. In conclusion, L. salicaria has a certain resistance to copper and chromium. Its chlorophyll content was rarely affected, the antioxidant enzyme system responded well, and could regulate the osmotic system for stress reaction. When the concentration of Cu²⁺ is lower than 5 mg/L and the concentration of Cr⁶⁺ is lower than 20 mg/L, its physiological and biochemical indicators are relatively less affected. Our findings provide theoretical basis for further research on the response of L. salicaria under the treatment of heavy metals, as well as its ecological application of water restoration.