Abstract:Based on the month cyclical changes of the isotopes of Poyang Lake Basin, we selected the deuterium isotope and oxygen isotope as a tracer to study the conversion relationship between the infiltration of precipitation, groundwater, rivers and lakes. The results indicate that in mid April the average values of δD and δ18O of lake water, river water and well water were(-2. 32%, -0. 42%), (-2. 86%, -0. 48%)and(-3. 18%, -0. 55%), respectively. The values of δD and δ18O scatter close to the Global Meteoric Water Line(GMWL). The isotopes in lake water are the most enriched, and the lake is not only supplied by rivers but also by precipitation around the lake. In late July, the δD and δ18O values of lake water, river water and well water are extremely depleted than that in mid April, which is consistent with the variation trend of isotopes in the precipitation. After experiencing the drought and high temperature, δD and δ18O values of lake water, river water and well water scatter along the evaporation line(EL2). The isotope data shows that the conversion between the well water and the river water is very frequent. Most of the precipitation infiltrates downward and becomes phreatic water, and then recharges river water through underground runoff. The cycle of precipitation conversing into the river water is about 1 months. During the rainy season from March to June, Poyang Lake greatly recharges the Yangtze River, which will affect the isotopic composition of the Yangtze River water.