On the basis of the climatic and water resource records in the recent 50 years (1961-2010) over the Erhai Lake Basin, the climatic characteristics and the impact on water resources by different climate types are analyzed, and the relationship between water resources and basin rainfall, temperature are addressed to quantitatively estimate the water resources of Erhai Lake. The results suggest that the temperature of the Erhai Lake Basin in the 50 years shows an increasing tendency with fluctuation and climate is warming obviously. The first decade of the 21st century is the warmest in the recent 50 years in the Erhai Lake Basin. The annual rainfall shows a tendency to decrease in general. The water resources of Erhai Lake have a remarkable positive correlation with the annual rainfall, but significantly negative with temperature. The climate was mainly cold and wet in the 1960s and 1970s in the Erhai Lake Basin, but getting warm after into 1980s and especially warm and dry in the first decade into the 21st century. The Erhai Lake water resources are in dry year when it is warm dry year, but in humid year when cold wet, and in normal year when the climate is normal. According to the prediction of future climate in Erhai Lake Basin and through the climatic type calculated by regression equation of climate forecast, the water resources can be estimated qualitatively and forecasted quantitatively whether it is dry year or humid year.