On June 25, 2020, Tianjin Xiqing was affected by a convective storm accompanied by a mesovortex (MV), which produced record-breaking gust (41.4 m?s-1) since the observation started in 1957. In order to improve the scientific understanding of extreme thunderstorm winds caused by such mesoscale vortex, the thermodynamic structure characteristics and maintenance mechanism of MV were analyzed by using the Variational Doppler Radar Analysis System (VDRAS) technique of radar data combined with multi-source observation data. The results show that the MV in this process was initially born at a height of 2.0 km, and the contracting and stretching vertical vortex rapidly descended to surface from 2.0 km height with the rotation speed increasing and vortex diameter contracting. During this process, the surface transition from warm and dry to cold and wet cyclonic vortex, extreme wind appeared in the overlap area of western of MV and rear inflow jet (RIJ). The evolution of MV was closely related to the different properties in convective storms. In the mature stage of MV, the vertical circulation was formed by tilt updraft (TUD), RIJ, front flank downdraft (FFD) and forward low-level inflow (FLI). During the strengthening and descent of MV, the rainwater evaporated and absorbed heat during its descent, leading to a significant enhancement in the intensity of RIJ and its continuous downward extension. The configuration of the cold pool and vertical wind shear plays crucial role in the evolution of MV: from the formation to development stage of MV, the cold pool and low-level vertical wind shear from 0-3 km height reach a stage of equilibrium; from the development to mature stage of MV, the cold pool and bulk vertical wind shear from 0-6 km height reach a balanced stage; from the mature to dissipation stage, the intensity of cold pool exceeds the bulk vertical wind shear, which is unfavorable for the storm development. Distinct from the ground-reaching RIJ associated with typical bow echo, the RIJ in this event did not reach the ground, but instead coupled with the vertical downdraft of MV in near an altitude of 1 km, generating a vertically downward perturbation pressure gradient force. Meanwhile, the drag effect of rainwater facilitated the strengthening of the downdraft. During its descent, evaporation and heat absorption weakened the cold pool, which in turn intensified the surface wind speed, collectively leading to the extreme gale.