Stable isotopes analysis, especially carbon and nitrogen, are now commonly used to study material circulation and energy flow within ecosystems. Carbon isotope ratios (δ13C) are used to trace food sources of consumers, while nitrogen isotope ratios (δ15N) are mainly used to quantify trophic levels of organisms. In this study 95 fish and other food web components from 4 sampling sites: Houkou County, Duchang County, Xingzi County and Wucheng Town, at north Poyang Lake in dry season were used as samples and their stable carbon and nitrogen isotope ratios were analyzed in laboratory. The results of carbon isotopic analyses, ranged from -27.5‰--24.6‰, indicated the δ13C values of particulate organic matter(POM) could identify different water sources in Ganjiang River, Xiushui River, Poyang Lake and the mixed area of Poyang Lake and Yangtze River. δ15N values in organisms in the heart of Poyang Lake national nature reserve were lower than those recorded in Xingzi and Duchang counties which were frequently disturbed by human activities i.e anthropogenic sewage increased δ15N in the ecosystem. The δ13C values of the same species of aquatic organism varied in different areas of the lake, however their relative trophic levels were similar according to the calculation of δ15N values.