Abstract: The weather scale and small-and-medium-scale system of the heavy rainstorm process in south Yunnan on August 7, 2020 is comprehensively analyzed based on the automatic weather station data, ERA5 reanalysis data, and sounding and CINRAD/CC Pu'er weather radar. The results show that: ① this heavy precipitation was a typical heavy rainfall process in warm areas; ② The 500 hPa east wind wave and 700 hPa low-vortex system were the main influencing systems, and the high-altitude radiation characteristics of 200 hPa strengthened the development of low-level systems; ③ Heavy precipitation mainly occurred in the background of high humidity, high energy and strong vertical movement of the atmospheric environment. Low pressure from The Bay of Bengal acted as a "water and gas pump", providing sufficient water vapor for local heavy precipitation in south Yunnan, and the divergence intensity of water vapor flux reached −4.6×10⁻⁶g·cm⁻²·hPa⁻¹·s⁻¹. The sub-height depression to the north of south Yunnan was conducive to the accumulation of unstable energy, so that the energy center was formed, and the area of ∑θ_se≥260 ℃ corresponded to the 6h heavy precipitation falling area on the ground. Heavy rainstorms were also accompanied by energy and strong warm advection transport; ④ The life history of the mesoscale convective system was complete and long, the echoes were born and disappeared in situ, the center was stable and less moving, the "train effect" was obvious, and the echoes of low-mass center warm clouds contributed to short-term and efficient precipitation, resulting in long duration of ground precipitation, with local high intensity. The three-dimensional inversion wind field in the vigorous development stage of convection had obvious small-scale secondary circulation and horizontal cyclonic convergence, and the projection positions of the two were consistent, showing the characteristics of three-dimensional motion of the convective system. Short-term heavy precipitation of more than 20 mm·h⁻¹ occurred near the ground projection, with a maximum of 78.6 mm·h⁻¹; ⑤ The very different influences of the topography of south Yunnan on the east (uplift) and west (lowering) airflows intensified the development of vertical movement in the convergence zone, and the two airflows met and confronted for a long time under the "trumpet" terrain barrier, which provided favorable topographic conditions for the formation of exceptionally heavy rainstorms.