Based on the monthly runoff data during 1950-2007 at Wujiadu Hydrologic Station in the Huaihe River Basin, the drought-flood abrupt alternation phenomena(including drought to flood and flood to drought) based on runoff was analyzed during the main rainy season(MJJA) by using long-and short-cycle runoff drought-flood abrupt alternation index(RDFAI). The results are as follows:1) the frequency of long-cycle runoff drought-flood abrupt alternations was higher in the period before 1986, and then decreased after the late 1980s; 2) Inter-annual changes of the short-cycle runoff drought-flood abrupt alternation phenomena between the adjacent months varied from each other, with the change between June and July being the most obvious one, and the long-term changes are similar to that of the long-cycle runoff drought-flood abrupt alternation phenomena; 3) Both the occurrence of long-and short-cycle runoff drought-flood abrupt alternation phenomena showed decreasing trends during the past 57 years, however, the total drought and total flood phenomena were on the rise; 4) During the 2000s, both the long-cycle and short-cycle runoff drought to flood abrupt alternation in June and July increased, and this might be one of the major reasons for the runoff increase during the rainy season at the same period.