This study examines the multi-scale processes responsible for an extreme thunderstorm gale event (peak wind speed 31.5 m·s-1) that occurred at Tianjin Airport on 4 August 2013. The study focus is on the synoptic background, structural characteristics of the storm, and dynamical mechanisms of the extreme wind. The results show that this event developed within a post-trough unstable environment, characterized by a pronounced dry layer in the mid-troposphere and moisture concentration below 925 hPa. Convective available potential energy exceeding 3000 J·kg-1, coupled with strong 0-6 km vertical wind shear and steep temperature lapse rates in the boundary layer, established a favorable environment for thunderstorm gales. The damaging winds originated from a squall line propagating rapidly from northwest to southeast. The passage of its leading gust front triggered the initial wind surge, while subsequent extreme winds during the second phase resulted from a downburst generated by an intensifying multi-cell in the squall line. Both the squall line and downburst exhibited significant mobility, with precipitation-induced evaporative cooling, hydrometeor loading, and mid-level convergence identified as primary drivers for the downburst formation.