Under the influence of an upper trough, a squall line occurred in Sichuan Basin on April 11,2022 , which caused extreme thunderstorm wind(37.4).Due to the lack of understanding of the rapid development mechanism of the squall line, there were large deviations in the forecast of short-time heavy rainfall and strong winds.Based on multi-source observation data and ERA5 reanalysis data,the circulation background,evolution and extinction of the squall line were analyzed.The results are as follows.The squall line occurred in the mutual coupling area of upper trough at 500hPa and the southerly jet at 700hPa.Upper layer divergence and lower layer convergence were significantly enhanced before the squall line formed,and the enhanced uplift provided dynamic conditions for the development of the storm.In south-central basin,the convective available potential energy(CAPE) was greater than 1000 , the deep and shallow vertical wind shears were greater than 15 , the height of wet bulb temperature 0℃ was 3.8km and the height of -20℃ was 7km, the vertical temperature lapse rate was 6.88℃, and a "bell mouth" was exist in temperature humidity profile below Lifting Condensation Level. Especially the vertical wind shear, middle dry layer and DCAPE approached or exceeded the extreme value, which provided favorable environmental conditions for the development of the squall line and the occurrence of strong thunderstorms gales.Convections in the northern segment of squall line were triggered and developed by the combination influence of terrain Longquan Mountains, cold pool and surface convergence line.In the south section, convections were uplifted by the dynamic action of the lower level.Due to the 700 hPa jet stream,surface cold pool and convergence line,two sections of linear convection were intensified and merged into a north-south squall line system with super-cell storms and bow echoes when moving eastward to the high energy and humidity areas in central basin.Super-cells before the formation of squall line and the echoes of the mature squall line both have overhang echos, weak echo regions, rear inflow and middle radial convergence.Downdraft formed by the rear inflow and dry curl in the middle troposphere makes the supercell storm and cold pool move faster than other parts. Then, a bow echo was formed.Due to the gale and precipitation of downburst, propagation velocity of the cold pool was significantly stronger than 0—3 km vertical wind shear which an important reason for the rapid weakening of squall line.