Abstract: According to the long-term series of climate and hydrological data of the Baixi reservoir in Ningbo City, we estimated the annual runoff distribution by the nonuniformity coefficient method and the fully regulated coefficient method. The interannual variation trend of precipitation and runoff in the Baixi reservoir were forecast by the extreme values ratio method, variation coefficient method, moving average method and cumulative anomaly method. Also, we detected the abrupt changes in the runoff by the Mann-Kendall test, sliding t-test and sequential clustering analysis, and analyzed the periodic change in the runoff by Morlet wavelet. The results show that as a result of Plum rains and typhoon events, the distribution of monthly runoff in the Baixi Reservoir displays a bimodal curve. The extremes ratio and variation coefficient of precipitation are smaller than that of the runoff. Therefore, the trend of precipitation is not identical to that of runoff at different spatial scales. In addition, annual runoff of the Baixi reservoir shows a slight upward trend with a change rate of 0.35 million m3/a. The average annual runoff is 254 million m3 and the average runoff during the past 10 years is 268 million m3. The abrupt change in the runoff occurs in 1971, and runoff shows changes in periodicity of 21,10 and 4 years.