Abstract: Extreme gale of 60.3 m·s^-1 was recorded by the national meteorological observation station at Lingui in Guangxi at 21:13 BT 21 March 2019, breaking the historical extreme value since the establishment of Guangxi meteorological stations. In this study, the development and formation of the extreme wind event were analyzed in detail by using a variety of observation data. The analysis indicates the following results. (1) The strong wind occurred at Lingui station was caused by a downburst introduced by a supercell storm, which is originated from convection in the warm zone before the cold front, and developed while meeting with cold air timely near the Lingui station. (2) Radar echoes show that the supercell has obvious radar characteristics such as hook echo, Mid-altitude Radial Convergence (MARC), strong divergence near the ground and decrease of reflectivity factor core. The flow field structure in the vertical direction of the storm reveals anticyclonic rotation or convergence at the top, MARC at the middle and cyclonic rotation at the bottom. (3) The strengthening of MARC led to the intensifying of rotation of the mesocyclone, the decrease of its diameter and the increase of its thickness. Especially, the strong mesocyclone near the ground level strengthens the downburst. (4) The environmental conditions indicated that there are excellent environmental conditions for producing thunderstorm gale and the potential of developing supercell storm over Lingui station. (5) The extreme precipitation had a drag effect on the gale. Under the action of topography, cold air wind has superimposed effect on extreme wind.