A blind spectrum sensing method and device based on fast Fourier transform. The method comprises: the spectrum sensing device receives a signal on an authorized spectrum band, calculates an autocorrelation coefficient of the received signal after sampling and filtering same, then performs a fast Fourier transform of the autocorrelation coefficient, acquires the modulus of the transform result, constructs determination variables on the basis of the modulus, and determine whether or not a signal of an authorized user is present. The method and device have the advantages of low calculation complexity, obviated need for authorization information characteristic, and insensitivity towards noise uncertainty, and are of great performance.