To further reveal lake-river relation between Poyang Lake and Yangtze River and watershed , the paper took Hukou hydrological station in Poyang Lake as the study object,and chose the impoundment time of Three Gorges Project (2003) as the cutoff point to analyze the quantitative relationship of water level-discharge.Then it applied the least squares method to fit the hydrological data series (monthly average water levels and flows) during 1978-2007 by linear fit, polynomial (cubic) fit and logistic fit. The optimal water level-discharge curve was selected by the coefficient R2. Meanwhile, this paper explored the influence factors of three kinds of fitting curves accuracy.and analyzed the trend of relationship between annually water levels and flows analyzed. The results showed that around 2003, the optimal water level and discharge curve was the polynomial (cubic) fit curve, while accuracy of logistic fit was the worst;the annually average water level at Hukou hydrological station showed a downward trend, while the annually average water flow showed a upward trend; the maximum annually average water level and flow both happened in 1998; the minimum annually average water level and flow took place in 2006 and 1979 respectively. The result can provide certain reference for the rational utilization of water resources and the protection of water environment at Poyang Lake area.