Based on ground-based and 1-km real-time merged precipitation products, as well as observations and reanalysis data of sounding, radar, satellite, ECMWF and ERA5, a 3D conceptual model is established for the two heavy precipitation processes with approximate rainband distribution before and during the Meiyu period in 2023. From the perspectives of synoptic systems, dynamics, thermodynamics and mesoscale processes, the formation mechanisms of the two processes are compared. The results are as follows. (1) Both heavy precipitation processes occur under the influence of cold air as well as the warm and moist airflow at the edge of the subtropical high, with roughly equivalent position of subtropical high trough line and a southwest jet stream south of the shear line. To the north of the shear line is southeasterly wind for the process before the Meiyu period, while it is northerly and easterly wind for the process during the Meiyu period. (2) Both processes occur in the area of high water vapor flux and near the convergence center of water vapor. For the process before the Meiyu period, the conditions of transfer of water vapor and convergence are poor, and the process is warm-sector convective precipitation; for the process during the Meiyu period, the upper-level trough is deeper and the cold front is moving southward on the ground, resulting in frontal precipitation. (3) Both processes occur under conditions of thermodynamic instability, and the conditions of thermodynamic instability and convective instability for the process during the Meiyu period are stronger than those before the Meiyu period. For the process before the Meiyu period, the precipitation in the former stage is mainly triggered by the convective clouds near the convergence line in the eastern part of Hubei and these clouds are combined with mesoscale convective clouds, while the latter stage is caused by the stable and less dynamic mesoscale convective system (MCS). For the process during the Meiyu period, the precipitation is mainly caused by the development of warm-sector convective clouds and frontal clouds. The echo bands of the heavy precipitation before the Meiyu period are composed of linear echoes and east-west echo bands, exhibiting the characteristics of multi-cell storms, while those of the precipitation during the Meiyu period contain larger-scale convective cells. (4) A 3D conceptual model for the formation of rainstorm is established to explain the mechanisms of heavy precipitation.