Water depth is an important environmental factor which affects growth, reproduction and distribution of submersed macrophytes. Increased water depth leads to changes of underwater light, wave and sediment properties, and may consequently affects physiological-biochemical characteristic of submersed macrophytes. To explore carbon (C), nitrogen (N) and phosphorus (P) stoichiometry of submersed macrophytes in response to various water depths and evaluate significance of these responses to fitness of submersed macrophytes, we investigated depth distribution of Vallisneria natans, a common submersed rosette macrophyte with strap-like leaves on a stunted basal stem, in a plateau deep-water lake, namely Lake Erhai, and measured leaf C, N, P concentrations of this species colonizing in different water depths. The results suggested that the colonization depths of V. natans were between 0.5 and 5.6 m. The depth range of optimum growth for V. natans was 1.5-3.4 m, where the plant reached its highest frequency of occurrence and relative biomass. The mean values of leaf C, N and P concentrations for V. natans were 356.10, 26.13 and 3.54 mg/g, respectively, and the ratios of C:N, C:P and N:P were 14.38, 113.46 and 7.85, respectively. N:P ratios were relatively stable, except for a higher mean value between 0.5 and 1.4 m than the other water depths. Leaf C concentration, C:N and C:P ratios decreased, while leaf N and P concentrations increased with increased water depth. These results indicated that leaf C, N, P stoichiometry of V. natans was significantly affected by water depth. In addition, we also found that increased water depth lead to convergent leaf nutrients in V. natans, which resulted in a weaker coupling of N and P concentrations in deep water than that in shallow water.