Abstract: Using hourly precipitation data from 65 national level ground meteorological stations in Hunan and the fifth generation European Centre for Medium-Range Weather Forecasts Re-Analysis data (ERA5) during the summer seasons (June to August) of 1971 to 2023, and employing the K-means clustering algorithm, this study investigated the spatial distribution characteristics of average summer precipitation, daily maximum precipitation, and precipitation frequency, as well as the diurnal variation characteristics and the formation cause of average hourly precipitation, precipitation frequency, and precipitation intensity during the summer seasons in Hunan. The results are as follows. (1) The average summer precipitation and maximum daily precipitation in Hunan generally show a pattern of more in the north and south, and less in the central region. The frequency of average summer precipitation is higher in southern and northwestern Hunan, lower in central and northeastern Hunan. The distribution of summer precipitation intensity is stronger in the north and weaker in the south. (2) The daily variations of average summer hourly precipitation, precipitation frequency, and precipitation intensity in Hunan during summer are bimodal, with the main peak appearing around 16:00 (Beijing Time, same below) and the secondary peak appearing around 00:00. (3) The total precipitation of events persisting 1~6 hours contribute more significantly to the precipitation peak at 00:00, while the total precipitation of long-duration events persisting over 6 hours are associated with greater contributions to the peak at 16:00. (4) Using the K-means clustering algorithm, 65 stations were classified into 3 regions. The daily variation curves of average summer hourly precipitation, precipitation frequency and precipitation intensity in Region 1 (R1) and Region 2 (R2) show a bimodal pattern, with the main peak of R1 appearing in the early morning and R2 appearing in the afternoon. Region 3 (R3) has a weak bimodal pattern of average summer hourly precipitation and frequency, with the main peak appearing in the afternoon. (5) The formation causes of precipitation peak formation in R1, R2, and R3 regions were preliminarily investigated through thermal, dynamic, and water vapor condition analysis. The peak precipitation in R1 area at midnight may be caused by dynamic forcing. In the early morning, the south wind strengthens, and the strongest low-level upward movement occurs. The water vapor flux input from the south also reaches its maximum value, and there is convergence of water vapor flux, which is conducive to the generation of precipitation. The peak precipitation in R2 and R3 regions in the afternoon may be triggered by local thermal instability. Due to surface heating in the afternoon, atmospheric stability is weak, which favors the development of convective precipitation.