Abstract: To reveal the climate characteristics of heauy drought and flood of Yangtze River valley and Yellow River valley in flood season, firstly we use Mexican Hat wavelet to analyze the precipitation data of Yangtze River valley and Yellow River valley from 1951 to 1999 and get the annual variation tendency of precipitation. Secondly, respectively divide Yangtze River valley and Yellow River valley into three reaches (upper, middle, lower reaches) and two reaches (upper-middle,down). With accepted standards of average precipitation R of each reach and month, the precipitation anomalous percentage is calculated. Thereby we obtain the time series date of each reach and month from 1951 to 1999 for heavy drought and flood. Finally, analyzing the time series data, we get the climate characteristics of heavy drought and flood of Yangtze River and Yellow River valley. The results in this paper improve our knowledge about heavy drought and flood.