The daily and the monthly precipitation data in Zaozhuang from 1958 to 2005 are analyzed. The results show that the period from the late 1950s to the mid 1960s was relatively wet and that from the early 1960s to the mid 1960s was a short dry period; the period from the mid 1970s to the late 1990s was a long dry period; then, floods occurred in the year of 2000, 2003 and 2005. The concept of “the number of equivalent heary rain days” is introduced, and the correlation of the number of the equivalent heary rain days and serious drought and flood years is studied. The precipitation of serious drought and flood years are closely correlated with the number of the equivalent heary rain days. The quantitative correlation for the number of the equivalent heary rain days and the annual precipitation is given. In a certain extent, drought/flood forecasts can be made according to the days of heavy rain in flood season.