This article adopts the method of hydroponic nutrient to study the effects of Ni concentrations added in different experiments(0, 0.05, 0.10, 0.15 and 0.20 mmol/L)on the Ni and nutrient elements contents, oxidative stress and antioxidant system in Hydrocharis dubia leaves. The results indicated that:(1)Ni content in leaves increases with the Ni concentration in solution.(2)Nutrient elements(Ca, Mg, K, Fe and Mn) in leaves are also affected by the solution. The content in Ca and Mg increases significantly with the increase of Ni concentration in solution. The content of K increases, but not significantly in leaves. Though Mn content of leaves decreases in the solution with higher Ni concentration, the treatment groups contain generally Mn in leaves higher than the control group. However, Fe content in leaves declines with the increasing of Ni concentration in solution.(3)Ni stress induces the apparent oxidative stress, characteristic of the increases of the productive rate of O₂^·- and the contents of H₂O₂ and MDA, and the obvious decreases of the contents of soluble protein and photosynthetic pigment in leaves.(4)With the increase of Ni concentration in solution, the activity of peroxidase in leaves increases gradually, while the activity of catalase is declined, followed by the firstly increasing and then decreasing activity of superoxide dismutase at 0.05 mmol/L in leaves. The content of vitamin E and flavonoids in leaves rises slowly with the increasing of Ni concentration in leaves. No apparent change of the glutathione is observed. The content of non-protein thiol and plant complexation both show increases at first. Total antioxidant capacity enhances firstly with Ni concentration in solution. Thus it can be seen that Ni stress causes the accumulation of Ni and the variation of nutrient elements in Hydrocharis dubia leaves, and generates obvious oxidative stress, breaking the balance of antioxidant system.