Abstract: In order to explore the effects of NO₃^- stress on photosynthetic characteristics and nitrogen metabolism, strawberry seedlings were grown in sand culture condition under different concentrations of NO₃^- (64, 112 and 160 mmol·L^-1) with the control of 16 mmol NO₃^-·L^-1. The results indicated that at the 8th day after treatment, with the increased NO₃^- concentration, the strawberry leaf net photosynthetic rate (P_n), stomatal conductance (g_s), PSⅡactual photochemical efficiency (Φ_PSⅡ), PSⅡmaximum photochemical efficiency (F_v/F_m), and photochemical quenching coefficient (q_P) significantly decreased, and decreased by 67.7%, 68.4%, 35.7%, 23.2% and 26.9%, respectively, when NO₃^- concentration reached 160 mmol·L^-1 compared with the control. The nonphotochemical quenching coefficient (q_N) increased by 4.4%, 10.9% and 75.8% respectively in the treatments of 64, 112 and 160 mmol NO₃^-·L^-1 compared with the control. The intercellular CO₂ concentration (C_i) decreased under low NO₃^- concentration stress and then increased under high NO₃^- concentration stress, while the stomatal limitation (L_s) was vice versa. With the increased NO₃^- concentration, the nitrate nitrogen, ammonia nitrogen, total nitrogen and Kjeldahl nitrogen contents in the strawberry leaves and roots increased, but the protein nitrogen content decreased. The activities of nitrate reductase (NR), glutamine sybthetase (GS), glutamate synthase (GOGAT) and glutamate dehydrogenase (GDH) increased at low NO₃^- concentration and then decreased at high NO₃^- concentration. Consequently, the net photosynthetic rate of strawberry seedling leaves decreased, the PSⅡ electron transfer was blocked, the nitrogen accumulated with the increasing NO₃- concentration, and the nitrogen metabolism enzyme activity decreased at high NO₃^- concentrations. When the NO₃^- concentration reached 64 mmol·L^-1 or higher in the nutrient solution, the growth of strawberry seedlings were inhibited significantly.