Poyang Lake is the largest freshwater lake in China, and the largest single area of habitat for migratory birds. The water level of Poyang Lake was declined continuous, and extreme droughts have frequently occurred in recent years, the structure and function of the wetland ecosystem were destroyed. In this paper, Stable oxygen isotopes was used as a tracer to identify composition of soil water, river water, ground water, and plants water. The focus was on characterize the variation with depth of the stable oxygen isotope composition and identifying the main sources of oxygen in soil water, ground water, river water and plants water, understanding the mechanisms of water movement among them. Soil water sampled at 10 cm intervals over the top 100 cm at two sections in the Poyang Lake wetland, and water samples collected from the plants, river water and ground water, were analysed for stable oxygen isotope composition, exploring the recharge and discharge of relationship between them. The results shown that the values of δ18O at depth of 0~30cm at section I were declined with increasing soil depth, the value of δ18O at depth of 0~40cm at section II had rare variation with increasing soil depth. The groundwater supply at section I was mainly influenced by precipitation, at section II was by precipitation and river water. The average value of δ18O in the domain species plants leaves of phalaris arundinacea, crex cinerascens, and phragmites communis was -0.9‰, -4.23‰, -5.25‰ respectively.