By using the conventional and unconventional intensive observation data, FY satellite data and NCEP/NCAR reanalysis data (1°×1°), a heavy rainfall process happened in Hunan in the main flood season of 2019 is analyzed and its causes are discussed. The results show that: the influence systems of this rainfall process were complex and changeable, which were composed of the warm zone rainstorm, middle cold advection intrusion rainstorm, and frontal rainstorm. The highest rainfall effectiveness occurred when the cold air invaded, and the strongest hourly rainfall intensity and accumulated rainfall reached the peak; the subtropical high was obviously strong, 24 longitudes west than the same period of previous year, and there were multiple active shortwave troughs around. The upper cold vortex activity was obvious, and the cold vortex and cold trough were superimposed in the same phase. The bottom of trough developed southward to the south of 30°N, and the northerly airflow at the back of the trough guided the cold air to penetrate southward and intersect with the southwest airflow at the edge of the subtropical high, which was the largescale circulation background of continuous heavy rainfall. Frequent activities of medium and smallscale systems and the development and merger of multiple MCC (Mesoscale Convective Complex) directly caused the rainstorm. The radar echo map shows the characteristics of lowcentroid precipitation and high rainfall effectiveness. When heavy rainfall occurred, the spatial distribution of divergence field and vertical velocity corresponded well, and the strong rising center and the nondivergence layer were relatively obvious.