Abstract: To gain a deep understanding of the characteristics of extreme precipitation in the Cangshan-Erhai Lake region, this study analyzed the impact system and refined characteristics of an extreme precipitation event in this region on September 18, 2020, combined with statistical and classification methods. The precipitation observation data from 46 meteorological observation stations, near-surface relative humidity and water vapor pressure data, doppler weather radar, boundary layer wind profile radar in Dali, and the fifth-generation European Centre for Medium-Range Weather Forecasts reanalysis (ERA5) data were used. The results are as follow. This precipitation process was a significant regional rainfall event (RRE). Under the influence of the convergence shear line, the mesoscale convective system near the shear line directly triggered this event. Sufficient convective triggering conditions existed in the boundary layer. The favorable system configuration enabled multiple small-scale convective systems to be generated during this process, resulting in precipitation above heavy rain in 30.5% of the stations in the region. The maximum accumulated precipitation in 19 h was 123.9 mm, with the maximum rainfall intensity of 33.6 mm•h^-1. Due to the differences in the origin, moving path, and intensity of the convective system, the spatiotemporal distribution of the precipitation was uneven and the scale was small. Strong precipitation was mainly concentrated in the east of Cangshan Mountain, while the precipitation in other regions was relatively weak. The convective system developed in the northern part of Erhai Lake usually moved fast with strong radar echo and relatively limited influence range. The strong convection generated on the west side of Erhai Lake and in the middle of Cangshan Mountain exhibited a prolonged lifetime and large influence range. The peak precipitation intensity appeared earlier in the northern part of Erhai Lake compared to the southern part. The precipitation intensity in the south of Erhai Lake declined slowly after reaching the peak. In other regions, the precipitation intensity dropped rapidly after the peak.