Abstract: In order to deeply understood the characteristics of extreme precipitation in Cangshan-Erhai Lake region, the precipitation observation data from 46 meteorological observation stations, relative humidity and water vapor pressure of the ground near, doppler weather radar, boundary layer wind profile radar in Dali station and ERA5 reanalysis data were used to analyzed the impact system and fine grained characteristics of an extreme precipitation event on September 18, 2020 in this region by statistical and classification methods. The results are as follows. 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 the heavy precipitation. There were sufficient convective triggering conditions in the boundary layer, and the favorable system configuration enabled multiple small-scale convective systems to be generated during this process, resulting in heavy rainfall above heavy rain in 30.5% of the stations in the region. The maximum accumulated precipitation in 19 h was 123.9 mm, and the maximum rainfall intensity was 33.6 mm·h⁻¹. Dued to the differences in the origin, moving path and intensity of the convective system, the spatio-temporal distribution of the precipitation was uneven and the scale was small. The strong precipitation was mainly concentrated in the east of Cangshan Mountain, while the precipitation in other regions was relatively small. The convective system developed in the northern part of Erhai Lake has fast moving speed, strong echo of radar and relatively small influence range. The strong convection generated on the west side of Erhai Lake in the middle of Cangshan Mountain has a long duration and large influence range. The peak precipitation intensity appeared earlier in the northern part of Erhai Lake than in the southern part of Erhai Lake. The precipitation intensity in the south of Erhai Lake fell slowly after reaching the peak, while the peak precipitation intensity in other regions decreased rapidly after appearing.