Abstract: The identification technology of frequency and damping ration based on complex Morlet wavelet transform is introduced, the principle of modal shape identification based on wavelet coefficients is deduced. In order to improve the identification precision of closely spaced modals, a method is developed to adaptive select the band wide and center frequent of mother wavelet based on minimum standard deviation. The natural frequency of large-span spatial structures are very low and closely, and it’s very difficult to excite the structures by exciter, in order to identify the modal parameter of large-span spatial structures, a combination method of NExT and wavelet is proposed. The results of numerical simulation and the analysis of data from the field test of Olympic venue NAC (National Aquatics Center) show that, it is effective to identify the low and closely spaced modal by complex Morlet wavelet.