The Sun Yat-sen Memorial Hall in Guangzhou, a nationally protected historic landmark with nearly a century of history, is famous for its unique architectural shape formed by a large-span octagonal steel roof truss. The dynamic performance of this steel roof system under the action of earthquakes and wind loads is critical to the structural safety of the building. To evaluate its safety under extreme loading conditions, this study investigated the structural dynamic characteristics of the steel truss system based on historical archives and 3D laser scanning data and updated an ABAQUS finite element model using results from Ambient Vibration Testing (AVT). Three ground motion records and wind loads with recurrence intervals of 10, 50, and 100 years were selected for nonlinear time-history analyses to investigate the coupled wind–earthquake response of the structure. The results indicate that, under a peak ground acceleration (PGA) of 0.4 g and a 100-year recurrence interval wind load, the maximum displacement at the roof of the steel truss system is 53.3 mm, and the maximum inter-story drift ratio is 1/125, both within the maximum displacement limit specified in the standard. Moreover, wind loads have a significant impact on structural displacement. Under the 100-year recurrence interval wind action, the root mean square (RMS) displacement reaches 13.05 mm, which is substantially higher than that caused by seismic action alone. The results demonstrate that the steel roof truss exhibits excellent wind and seismic resistance, providing critical technical support for the safety evaluation and preservation of historic buildings.