In river reaches restored by reclaimed water, Phragmites australis showed distinct carbon (C) and nitrogen (N) stoichiometry due to the long-term influence of reclaimed water with high nitrogen. To identify the C and N stoichiometric characteristics of P. australis and its response to high N environment, contents of C and N and carbon: nitrogen ratio (C/N) in river water, soil and organs of P. australis (root, stem, and leaf) were analyzed in the growing seasons (May, July, and September) of P. australis. The results showed that the C, N contents and C/N ratio in river water ranged between 22.20-37.25 mg/L, 2.24-11.20 mg/L, and 3.33-9.92, respectively. The contents in soil were 5.69-35.17 mg/g for C, 0.28-2.63 mg/g for N, and 8.77-25.39 for C/N ratio, respectively. At all sampling sites during the growing seasons, mean values of C contents in roots, stems, and leaves of P. australis were (170.84±63.56), (369.02±39.12), and (431.80±96.70) mg/g, respectively; for N contents, they were (8.20±3.96), (14.11±6.22), and (30.73±8.66) mg/g, respectively; for C/N ratios, they were respective 23.89±12.84, 32.65±18.48, and 15.21±5.60. The C and N stoichiometry in different organs of P. australis had significantly seasonal differences (P<0.05) in variance analysis, which was mainly caused by the physiological processes of P. australis in the growing seasons. The C and N stoichiometry in the environment had significantly spatial differences (P<0.05), leading to significant decrease of N content and C/N ratio in leaf of P. australis from upstream to downstream (P<0.05). Regression analysis indicated that the C and N contents in soil and river water could explain 71.0% of the variances of N content in P. australis leaf (P<0.05), while C and N contents in soil and the N content in river water could explain 82.6% of the variances of C/N ratio in P. australis leaf (P<0.05). Significantly positive correlation between N in river water and N in soil (P<0.05) were implied by correlation analysis, indicating close N exchange between river water and soil. Under the influence of the reclaimed water with high nitrogen, it showed strong N supplying capacity by soil, which caused high N content in P. australis leaf, and lower C content in root compared with stem and leaf of P. australis. Consequently, P. australis had strong storage capacity of N in the river reaches restored by the reclaimed water since its C and N stoichiometry showed strong responsiveness to high N environment.