Abstract: Based on the precipitation of 7 national basic stations in Chuzhou city during 1970—2019, Ensemble Empirical Mode Decomposition（EEMD） was used to analyze the nonlinear variation characteristics of the annual precipitation and flood season precipitation. The results showed that taking Chuzhou station as an example, the precipitation had short periods of 2.3 years and 8.0 years which were dominant, as well as the long-term oscillation 16 years and 32 years. The contribution rate of precipitation in the flood season was above 60% of the annual precipitation, and generally speaking, the spatial distribution of precipitation in flood season was more southeast and less northwest;The ratio of rainstorm precipitation in flood season to precipitation in flood season was above 33%. In the past 50 years, the frequency of rainstorms in 7 national stations in the flood season all showed an increasing trend, except Tianchang station and Laian station, while the frequency of light rainstorms in the flood season all showed a decreasing trend.

Key words: annual precipitation, precipitation in the flood season, EEMD method, Chuzhou city