A combination of fractional Fourier transform (FRFT) and time-frequency method is presented to identify ambient excited modes. In this method, Gabor expansion is applied to identify natural frequencies and damping ratios. The signal autocorrelation can enhance energy distribution of each channel signal, which can help to identify parameter. FRFT is a good tool to estimate excitation signal. A simulation example is presented to demonstrate the performance of this method. The results have shown that the proposed method gives a reasonable estimation of modal parameters and excitation signal from response signals.