Making use of conventional ground observation, upper air observation and ERA5 reanalysis data, the regional heavy rain and its associated short-time heavy rainfall processes in Southwest Shandong Province on July 22 (referred to as “7·22” process) and August 6-7 (referred to as “8·6” process) in 2020 are diagnostically analyzed. The results show that: the “7·22” process was a surface cyclone precipitation process, and heavy rainstorms mainly occurred from the cyclone’s centre to the inverted trough moving to the front right part. The short-time heavy precipitation was caused by the enhancement of inertia instability after the convective instability was triggered. The “8·6” process was a precipitation process in the warm area of the WPSH edge, and heavy rainstorms mainly occurred in the front of the low-level jet and near the surface convergence line. The short-time heavy precipitation was caused by the triggering and release of convective instability. In the “7·22” process, the warm-wet jet was stronger, and the divergence of water vapour flux and dynamic conditions were significantly stronger than those in the process of “8·6”. The strong convergence zone at very low levels, the greater value area of vapor flux divergence, the strong frontogenesis area on the edge of greater value area of horizontal kinetic energy, and the small value area of |MPV2| on the edge of great value area of MPV are very indicative for the emergence of short-time strong rainfall. Both processes show that the combination of vertical upward movement and deep wet area is a good indicator of short-time heavy precipitation occurrence time.