Abstract: The study on ecological stoichiometry of alien species can help to understand the mechanism of successful invasion of alien species from the view of ecological stoichiometry. In this study, C, N and P content and their ratio in organs of alien species Rhynchelytrum repens and native species Digitaria multiflorum were determined in order to reveal the carbon, nitrogen and phosphorus stoichiometric characteristics and their nutrition strategy of alien species R. repens. The results show that: (1) The stems-P content of R. repens varies significantly, that the stem-P content of heavy invasive plant (2.858 g·kg^-1) was significantly higher than that of the other two invasive plants (1.197 and 1.284 g·kg^-1, respectively), suggesting that with the increasing of invasive degree the plant distributes more P to the stem. (2) Under three different invasive degrees, N content of leaf (14.35-16.55 g·kg^-1) was higher than that of root (5.376-6.057 g·kg^-1) and stem (4.204-4.238 g·kg^-1), and at heavy invasive site, P content in leaf (2.949 g·kg^-1) and stem (2.858 g·kg^-1) were higher than that of root (1.261 g·kg^-1). At medium and light invasion sites, P content of leaf were higher than that of stem and root. (3) Under the three different invasion degrees, N:P in stem were significant lower than that in root and leaf. Under medium and light invasion degrees, C:P in leaf were lower than that in root and stem. At heavy invasion sites, C:P of stem and leaf were lower than that of root, implying that the growth rate of stem increase with the invasive degree. (4) N and P content in stem, N content in leaf of R. repens were significantly higher than that of D. multiflorum, implying that R. repens has a strong ability to absorb and utilize environmental N and P elements. There was no significant difference in C:N of root, stem and leaf between R. repens and D. multiflorum. It is worth to note that C:P, N:P in stem of R. repens were significant lower than that of D. multiflorum, showing that the growth rate of stem for R. repens may be greater than that for D. multiflorum. (5) Comprehensive analysis of stoichiometric characteristics indicates that strong absorption and utilization of N and P elements, and rapid growth rate of stem contribute to competitive advantage of R.repens, to defeat the native species through "Growth Competition Strategy".