Based on NCEP grid data and routine observational data, the characteristics of the potential vorticity (PV) of heavy rainfall occurring in Yunnan Province during autumn of 2004 are analyzed. The results show that both DPV and MPV can well present the features of the weather systems. The DPV reflects both convergence intensity between Yunnan Province and Guizhou Province and surface cold air moving activities more particularly. The MPV can reflect well cold and warm air flowing characteristics. During the heavy rainfall in the upper troposphere the strong DPV and MPV tend downwards to the low-level, and vice MPV in the lower troposphere stretch up. The direction and intensity changes of the big center of DPV and MPV in the upper troposphere tend to downward the lower-levels are consistent with the moving direction of heavy rainfall belts and the variation of the rain intensity. The origin of the middle tropospheric strong DPV lies in the east of Sichuan Province in this rainfall process, which indicates some relation between the heavy rain in the eastern Sichuan Province during 2-6 September and the rainfall process in Yunnan Province.