In order to assess the effect of future climatic variation on runoff, the paper analyzed the temporal and spatial variation trends of climate and established a statistical model to study its impacts on the runoff by using the observational data of weather station and the annual runoff series (1961-2010) of five hydrological gauging stations within Poyang Lake watershed. The results indicated that annual temperature presents the obvious rising trend;it presents the significant increase especially in winter. Precipitation and its intensity showed a slightly upward trend, and the risk of flood is increasing. The runoff in Poyang Lake watershed showed the increase trend, the temporal and spatial distribution became more unbalanced under the influence of rising temperature and increasing precipitation. Model results show that the relationship between runoff and precipitation is non-linear. Runoff has a strong sensitivity to rainfall variation. Increased precipitation has been more significant influence on runoff than decreased precipitation, which indicated that the precipitation changes played an important role in causing different effects of runoff. Under the condition of specified precipitation scenarios, the shifting relationship between the runoff and the temperature is linear. It is not obvious that temperature change impacts runoff. Under the future scenarios of climate change,the runoff Poyang Lake watershed appears obvious increase trend under the scenarios of high discharge A2and RCP8.5, while the runoff is lower than other emission scenarios until 2050.