Abstract: As a method of time-frequency analysis，spectrogram will be affected by cross-terms while analysing signals，especially for signals who are aneared，and also frequency resolutions will be influenced.This paper proposes combining fractional Fourier transform with spectrogram towards multi-component signals analysis.First，it obtains the optimal factional orders by using the second order fractional Fourier transform moments，and makes a fractional Fourier transform for multi-component signals according to the gained order，then gives spectrogram analysis based on the FrFT.Simulative examples indicate that the proposed method can effectively distinguish multi-component chirp signals，and the cross-terms can be suppressed availably.