Potamogeton crispus plants exposed to 1, 3, 5, 7mg/L Hg²⁺ for 7d were analyzed with reference to its toxic impact on mineral nutrition adsorption, total chlorophyll content, soluble protein, lipid peroxidation (MDA), proline, GSH and ultrastructure under lab conditions. The results revealed that, with the rise of Hg²⁺ concentration in culture medium, (1)the content of chlorophyll and soluble protein decreased gradually, while that of MDA and free proline increased and GSH content enhanced progressively up to 5 mg/L Hg²⁺ and followed by a decline at higher dose. (2)The addition of Hg²⁺ also affected the absorption of mineral nutrients; it mainly increased the absorption of Ca²⁺, Fe³⁺, Mg²⁺ and Zn²⁺, but reduced that of P and K⁺. (3) The amount and intensity of protein/peptide band decreased gradually with augment of Hg²⁺ concentration was observed in SDS-PAGE, respectively, and two polypeptides with apparent molecular weights 83.6kDa and 51.3kDa disappeared significantly in fronds treated with 5 and 7 mg/L Hg²⁺. (4) Transmission electron microscope observation indicated that Hg²⁺ imposed injury action on ultrastructure of leaf cells, such as swelling of chloroplast, breakage and disappearance of chloroplast envelope and disaggregation in the end. The conclusion could be reached that the death of plant was resulted from destruction of structure foundation of physiological function, unbalance of ion equilibrium and disorder of physiological metabolism. The lethal concentration scope of Hg²⁺ to Potamogeton crispus was 1～3 mg/L based on the experiment results.