Abstract: The effects of water depth on the growth of Vallisneria natans and photosynthetic systemⅡ photochemical characteristics of the leaves were investigated at three depths of 0.6, 1.3 and 2.0 m. The rapid fluorescence induction kinetics curves (OJIP) of the leaves were measured with Plant Efficiency Analyzer and analyzed with JIPtest. The results indicated that the light intensities at water depths of 0.6, 1.3 and 2.0 m were obviously different and the growth of V. natans was restricted under water depth of 2.0 m. Biomass, number of ramets, number of leaves, total root length, root surface area and other morphological indices decreased significantly with the increasing water depth, and the maximum leaf length, average leaf length, maximum leaf width changed insignificantly with the water depth. With the increasing water depth, absorption flux per reaction center (ABS/RC), trapped energy flux per RC (TR₀/RC), electron transport flux per RC (ET₀/RC), reduction of end acceptors at photosynthetic system Ⅰ(PSⅠ) electron acceptor side per RC (RE₀/RC) decreased significantly. The dissipated energy flux per RC (DI₀/RC) also decreased significantly, which led to no obvious difference in quantum yield for the reduction of end acceptors of PSⅠ per photon absorbed (φ_R0) and the efficiency for the trapped exciton to move an electron into the electron transport chain from Q_A^- to the PSⅠ end electron acceptors (δ_R0). Because the amount of active PSⅡ RCs per CS increased significantly, photosynthesis per area of V. natans grown at 2.0 m was significantly greater than that of V. natans grown at 0.6 m. The performance index PI_abs, PI_cs, PI_abs,total photochemistry efficiency of leaves of V. natans grown at 2.0 m was significantly increased, suggesting that light stress may promote a more efficient conversion of light energy to active chemical energy. V. natans leaves accommodate the low light intensity environment through activating inactive reaction centers but not through improving light utilization efficiency per reaction center, and the water depth of 1.3 m may be more suitable for the growth of V. natans.