Abstract: Based on NCEP 1°× 1° 6h reanalysis data, satellite cloud image data and conventional observation data, a shear line rainstorm occurred in Liangshan Prefecture from June 29 to 30, 2020 is analyzed. The results show that the plateau trough and the low-level shear line are the main influence systems of the rainstorm weather, the high-level divergence of the South Asia high is conducive to the triggering and maintenance of the rainstorm. The obvious water vapor transport and convergence, unstable stratification with high-energy and high humidity, and the strong vertical upward movement provide favorable conditions for the occurrence of the rainstorm. The configuration of MPV1>0 in the upper troposphere, MPV1<0 in the middle and lower troposphere, MPV1>0 in the middle and lower troposphere and MPV2<0 is beneficial to the occurrence of rainstorm. MCC formed by the development and combination of three mesoscale convective clouds is the direct influence system of the rainstorm process, and heavy rainfall often occurs in the low value area of TBB and the high value area of gradient.