The typical precipitation processes in the pre-flood of South China and precipitation processes of typhoons in the post-flood period of South China have different water vapor transport characteristics. In this research, the water vapor transport characteristics of the representative precipitation cases in the two circumstances were compared using the fifth generation ECMWF reanalysis (ERA5) and Late Run of Integrated Multi-satellitE Retrievals for GPM (IMERG-L). The water vapor transport channel of the precipitation process of the typhoon was stronger and higher than that in the pre-flood period of South China, and the distribution of water vapor flux convergence was also higher. The maximum value of water vapor flux of pre-flood case was related to the wind speed and specific humidity both in the boundary layer (950 hPa). For the typhoon case, the maximum value of water vapor flux was related to the wind speed in the boundary layer, whereas it was related to the specific humidity in the middle and low layer (700 hPa). These distinctions can help us quickly find the probably locations and impact factors of the maximum values of water vapor flux during precipitation processes in the pre-flood of South China and precipitation processes of typhoons in the post-flood period of South China on different pressure surfaces to the greatest extent and predict the intensities of different water vapor transport channels.