Traditional AVO theory only focuses on the petrophysical characteristics of two sides of an interface in spite of the layer thickness and other wave fields as well as attenuation and dispersion of seismic waves in reservoir so that there are many problems in the actual application of the technique. Seismic waves are the comprehensive responses of several thin sand/shale interbeds. After Fourier transformation, the reflective wave from each thin bed will respond to a specific frequency component, which is unique in frequency domain. By combining the spectral decomposition and AVO technique, this study on the frequency dependent AVO will be one of the effective tools in solving the seismic AVO identification issue in a thin interbed gas reservoir. A brief introduction of AVO technology is given while the problems in traditional AVO analysis are illuminated. The relationship between seismic AVO and frequency is discussed and the reason of frequency dependent AVO analysis is indicated. The time-frequency analysis method is also discussed.