NO₃^-low affinity absorption dynamics of Suaeda physophora Pall. and mechanism of the high NO₃^- absorption efficiency were studied using the conventional ion depletion method with Gossypium hirsutum L. as control in the nutrient solutions different in Cl^- and NO₃^--N concentration. Results show that the NO₃^- uptake rate of S. physophora and G. hirsutum increased linearly with KNO₃ concentration from 1 to 50 mmol L-1 in the solution. But the net NO₃^- uptake rate and nitrate reductase activity were significantly higher in S. physophora than in G. hirsutum, which implies that S. physophora has a higher demand for nitrate than G. hirsutum does. After 2 h of pre-treatment with 10 mmol L^-1 KNO₃, the total nitrogen concentrations increased by 30.6% and 36.8% in the shoots of G. hirsutum and S. physophora, respectively, meanwhile, the net NO₃^- uptake rates of the two reduced by 46.6% and 45.5%, respectively, which suggests that N uptake of the two species were regulated by negative feedback of the N nutrition of these plants. When G. hirsutum and S. physophora were put under NaCl stress for 30 days, NO₃^- uptake was significantly inhibited, more in G. hirsutum than in S. physophora. The net NO₃^- uptake rate exhibited a significant negative correlation with Cl^- concentration in the roots of G. hirsutum and S. physophora, indicating that the ablility of the root of S. physophora to resist Cl^- was higher than that of G. hirsutum. Temporary NaCl or KCl stress for 2 hours did not affect much the net NO₃^- uptake of S. physophora, but did decrease that of G. hirsutum by 43.8% and 37.5%, respectively. The findings indicate that the high-efficiency nitrate uptake by S. physophora roots is related to the high N demand and Cl^- accumulation of the plant, and Cl^- concentration in the nutrient solution does not have much impact on NO₃^- low-affinity transport system.