Abstract: It is important to determine the wind-induced response accurately and formulate the component of equivalent static wind loads of large span roofs reasonably. Ritz Vector Method and Proper Orthogonal Decomposition (POD) technique are employed to analyze wind-induced response of these structures, in order to take into account the multimode buffeting response and the case that structures vibrate with high frequency modes. The resonant component of equivalent static wind load can be formulated in terms of these modal inertia loadings. Moreover, the resonant component of equivalent static wind loads is analyzed for a saddle-shape cable structures with this method. The result shows that it is effective and efficient to solve these problems with this method.