Based on Fractional Fourier Transform(FRFT),a new method for automatic identification of communication modulated signal is put forward.The maximum value of the FRFT spectral power density of the intercepted signal is used to the identification algorithm of analog and digital modulation types.FRFT spectral characteristics of common modulated signals are analyzed in the new method,and a good classification effect can be got because the gradual changing characteristics of the signal from time domain to frequen...