Abstract: Using high altitude detection data, ground encryption regional automatic weather station data, NCEP1°×1°reanalysis data and FY-4A infrared cloud image data, Doppler weather radar data and wind profile radar data, the temporal and spatial distribution of precipitation, circulation background and storm system evolution of a regional rainstorm process in Sichuan Basin from 11 to 13 August 2020 were analyzed, and the role of low-altitude jet in this process was discussed. The results show that: (1) This process occurred in the background of 'east-high-pressure and west-low-pressure', the main influencing factors were 500hPa low trough, subtropical high and southwest vortex. (2) The emergence of low-level jet was conducive to the formation of positive vorticity column and the establishment of upflow branch, and the topographic action in the northwest of the basin enhanced the upward convergence. (3) Low level jet brought water vapor and unstable energy to the rainstorm area. (4) The influence of jet on precipitation storm system could be divided into two stages. The first stage was dominated by southeast jet. On the one hand, it led the convective system to move and strengthen in the northwest direction, and on the other hand, it triggered the strong convective echo zone in the northwest of Sichuan Basin. The second stage was dominated by the northeast jet in the northwest quadrant of the southwest vortex. On the one hand, strong dynamic convergence was formed on the left side of the jet outlet, and on the other hand, warm and humid air in the south of the vortex was transported to MCS. During the whole influence process, the lower boundary of the main body of the jet stream decreased from 3000m to 600m, and the dominant wind direction changed from southeast to northwest. (5) When the low-level jet intensified, MCS was maintained in the upstream area of the representative station, showing the characteristics of quasi-static backward propagation. When the low-level jet stream weakened, the quasi-static state of MCS was broken, and the convective system moved quickly to the representative station, bringing short-term heavy precipitation. (6) The Longquan Mountain increased the cyclonic angle of the northeast jet stream in the surface layer and enhanced the horizontal convergence. When MCS passed over Longquan Mountain, it was a topographic convergence zone, and the new cells were excited to form on the west side of the piedmont and move northeast along the mountain.