Abstract: Large-span saddle-backed cable net roofs are apt to have many frequencies in a narrow frequency range. Analyzing the wind-induced response of roof using mode superposition method with just the first several modes would not lead to accurate results. No generally accepted method exists regarding the necessary number of modes required for such analysis at present. An effective method - Ritz-POD method - to choose the significant modes is proposed. The method is used in the wind-induced response analysis of a saddle-backed cable net roof. The result is compared with that of the traditional mode superposition method, proving effectiveness and accuracy of the method.