Abstract: Affected by the residual vortex of Typhoon “Gaemi”, Xupu in Hunan Province experienced a Record-Breaking extreme hourly rainfall (EHR) of 120.1mm·h-1 on July 28, 2024. To get a deep understanding of the development mechanism of HER and improve the analysis and forecasting ability of EHR, multi-source observations and ERA5 reanalysis data are comprehensively used to analyze the causes and microphysical characteristics of EHR. The results show that under the favorable environmental conditions of stratification, energy, and water vapor, the convergence between the southwest moisture transport from the south side of the typhoon residual vortex and the northerly moisture transport from the west side of the residual vortex triggered the occurrence of extreme hourly rainfall. The EHR is caused by a quasi-stationary β-scale Mesoscale Convective System (MCS). On the radar echo map, this MCS shows as the merging process of two strong storm cells embedded in the mixed cloud echo, which belongs to the low-centroid, high-efficiency warm cloud precipitation echo. The vertical structure characterized by low-level convergence and mid-high-level divergence is conducive to the maintenance of ascending motion. The maintenance of the coupling situation between mesoscale vortex (MV) and secondary circulation strengthens the vertical upward movement within the storms, facilitating the transport of low-level warm and humid air to the updrafts, consequently generating and maintaining extreme rainfall rates, and leading to the occurrence of EHR. During EHR, the diameter and concentration of raindrops increase, mainly due to the collision and growth of warm rain. The rainfall is primarily contributed by raindrops with diameters greater than 1 mm, among which the contribution rate of rainfall in the range of (1, 3 mm accounts for about 80%. Finally, a conceptual model of the EHR was summarized, which provides a reference for future weather analysis and forecasting research.