On August 3, 2021, there was a strong thunderstorm and gale weather case with shortterm heavy rainfall and a downburst in Liuzhou. In this case, the cause of the downburst is analyzed by using observation data, minutelevel data from the Liuzhou automatic station, radar, wind profile and other data. The results show that: (1) This case was triggered by the rise of the surface mesoscale convergence line, under the background of the middle and lower layers of northeast airflow between the continental high and the tropical convergence zone, and favourable environmental conditions such as weak vertical wind shear, strong unstable energy, deep dry air source, and dry adiabatic decline near the ground. (2) The initial echo of the downburst had the characteristics of the pulse storm and then developed into the multi-cell storm. Before the downburst, the reflectivity core decreased, and the lower-level inflow and the middle-level radial convergence increased. Its vertical structure showed lower-level divergence, middle-level convergence, and middle-upper-level convergence rotation. (3) The wind profile radar wind field had obvious upper air momentum downward transmission and lower-level wind speed reduction before the ground gale appeared. The gale appeared at the time when the lower-level wind speed started to increase, earlier than the time when the lower-level wind speed was strongest. (4) The downburst was related to the drag and negative buoyancy of precipitation particles. The topography made the strong convection echo move along the topography, and the downhill topography and the isthmus effect had a superposition effect on the formation of extreme gales.