Abstract: The causes and multi-scale characteristics of the short-term heavy rainfall process in Zigong City, Sichuan Province on August 12, 2020 were studied by using conventional weather observation data, ERA5 reanalysis data of 0.5° × 0.5°, ground automatic station encryption data and satellite cloud image products. The results show that the combination of high-altitude low trough and low-level convergence system with low-altitude jet is a large-scale circulation system in this rainstorm weather process, and low-altitude jet provides sufficient water vapor and energy for heavy rainfall areas. The enhanced convergence ascending dynamic effect, the rapid growth of water vapor content and the increase of unstable energy provide conditions for convective heavy rainfall. A strong meso-β scale MCC was formed by the merging and strengthening of two convective clouds. The heavy rainfall area was located near the center of the minimum cloud top brightness temperature of MCC, which reached −82 °C. The surface mesoscale convergence line plays a role in triggering and strengthening convective systems in the short-term heavy rainfall.