Abstract: Based on the ERA5 (0.25°×0.25°) hourly reanalysis data, this study analyzes two high-impact Southwest China Vortex (SWV) processes with long-distance movement and stagnation over a local area. It is suggested that two physical variables, namely, the low- to mid-level convergence and pseudoequivalent potential temperature, are the key factors influencing the development and evolution of the vortex. According to the findings, a vortex development index is defined in this study. By comparing the vortex development index with the evolution of the SWV and precipitation, the following results were obtained. (1) The vortex development index can indicate the development and evolution trend of the intensity and position of the vortex, whether it is a long-distance moving or a local stationary SWV process. In addition, the index can reveal multicore vortices during intense vortex events and the moving mechanism of the SWV. (2) The vortex development index not only indicates the intensity and coverage area of vortex precipitation but also reflects the coexistence phenomenon between SWV and precipitation, thereby providing a possible explanation for the “rain-induced vortex” and “vortex-induced rain” phenomena. The results of this study suggest the positive significance of the vortex development index in forecasting the precipitation distribution and the position of the precipitation center of high-impact SWV heavy rainfall events.