Ultra-high voltage (UHV) long-span (LS) transmission lines, characterized by large tower heights and long spans, are highly susceptible to wind loads. Wind fragility analysis is an essential method to assess their reliability under wind-induced actions. Using an UHV-LS transmission tower in Anhui Province as a case study, this research applies random wind vibration response theory and China’s current overhead transmission line loading specifications to determine the structural response distribution under wind loads. The analysis incorporates uncertainties in structural material properties to establish the probabilistic distribution of wind load-carrying capacity. Performance levels are quantitatively evaluated using tower-top displacement and corrected inter-segment displacement angles as indicators, leading to the development of wind fragility curves. The results indicate that the quasi-static wind effect distribution of the transmission tower-line system can be obtained using probability-based methods for the first time. The fragility assessment shows that performance levels based on tower-top displacement are more conservative than those based on modified inter-segment displacement angles. Additionally, as structural damage intensifies, the influence of material uncertainty on load-bearing capacity becomes more pronounced. Overall, wind fragility analysis shows that UHV towers exhibit good wind reliability under design wind loads, although their wind-induced failure shows brittle characteristics.