Wind loading on a lattice steel transmission tower structure is affected by the wind field, structural parameters, and the geo-spatial arrangement of the transmission line. However, it has not been sufficiently studied due to the key issues in performance evaluation and uncertainty treatment for transmission towers. Besides, most current uncertainty treatment only considers the tower itself although the transmission tower is part of an interconnected tower-line system that has complex interactions with wind environment. Therefore, this research seeks to develop a systematic wind-induced performance evaluation framework for transmission tower-line systems. Therefore, appropriate fragility assessment of the practical transmission tower with the consideration of the transmission line, exposing it to various directions of strong wind can be conducted using the established framework. It was found that the wind attack angle imposes a significant effect on the fragility of the transmission tower-line system and the wind attack angle of 0o (perpendicular to transmission lines) is the most unfavorable wind attack angle of the simulated tower-line system and the fragility curve shifts right with an increase in the wind attack angle.