Abstract: The characteristics of drought and flood over east Yunnan Province, China in spring in recent 53 years were analyzed. Yunnan was divided into three rainfall climate regions by REOF method based on the data of rainfall in spring, and the location and area range of the eastern region was determined. The index of PDSI was chosen to describe drought and flood in east Yunnan after compared with other two kinds of drought index only based on rainfall. By applying Morlet Wavelet Method, it was found that there was an obvious 14 years fluctuation period of drought and flood in east Yunnan in recent 53 years, and the time series could be divided into three periods: drought period from 1958 to 1980, flood period from 1981 to 2000, and another drought period after 2000. The synthetic analysis on drought and flood over east Yunnan showed that there were two parallel zonal waves in the circulation background anomaly fields of geoheight, zonal wind and air temperature. In flood years, the highlatitude wave was positive but the midlatitude one was negative for geoheight anomaly field at 500 hPa, which revealed that the low systems over Yunnan were active. For zonal wind anomaly field at 500 hPa, the highmid latitude wave was minus and the midlow latitude one was plus, which revealed that the south branch trough over the south of the Qinghai-Tibetan was strong at both velocity and transferred moisture amount. For the temperature anomaly field at 700 hPa, the highlatitude wave was positive and the midlatitude one was negative, which showed that the temperature over Yunnan was lower than normal and formed a temperature front with warmhumid air mass of subtropic high over lowlatitude ocean. It was benefit to the generation of front precipitation in east Yunnan. In drought years, properties of all the factors were opposite to those in flood years for the two parallel zonal waves at anomaly fields. It needs to be emphasized that a southward refraction occurred when the upstream zonal wind was blocked by the southwest boundary of the Qinghai-Tibetan Plateau. Strong wind in flood years and weak wind in drought years affected directly by the intensity of the south branch trough, and the upstream wind intensity and the south branch trough intensity were proportional. The key precipitation system over east Yunnan in spring was the Kunming quasistationary front. Within the background anomaly waves, the front showed that its occurring frequency and duration were higher and longer in flood years than those in drought years.