Abstract: An experiment was designed to have 5 treatments, i.e. 0, 1, 2, 4 and 6 mg•L^-1 of ρ (Cu²⁺) to explore effects of Cu²⁺ on growth and physiological indices of Vallisneria natans. Results show that the effect of Cu²⁺ stress on V. natans was significant. When ρ (Cu²⁺) was 2 mg•L^-1, growth of V. natans was inhibited with the plants shortened in plant height and reduced in fresh weight, but they still survived. When ρ (Cu²⁺) was 4 mg•L^-1, the phenomena of inhibition became more obvious on the plants, of which the outer leaves began to decay and turn black after 30 days of stress. A trace amount of Cu²⁺ was conducive to activation of catalase (CAT) and enhancement of stress resistance of the plants. The experiment found that CAT reacted earlier than MDA and H₂O₂ did, therefore, it was more accurate and effective to monitor changes in CAT activity for physiological studies of stress resistance of V. natans. As 2 mg•L^-1 of ρ (Cu²⁺) can inhibit the growth of V. natans, so that, it is not suitable to build any Cu²⁺-contaminated wastewater purification system with V. natans as submerged vegetation when Cu²⁺ concentration in the wastewater is higher than 2 mg•L^-1.