The invention relates to a method for detecting a frequency spectrum based on the adjacent phase differences. The method comprises the steps of calculating a judgment threshold Th as specified in the specification according to the length N+1 of determined sampled chips and the false alarm probability P required by the detection, conducting IQ data sampling on a signal of a target frequency band, calculating the accumulative amount Psi of the adjacent phase differences of the sampling chips, and judging whether a signal of a main user exists or not according to the accumulative amount Psi of the adjacent phase differences of the sampling chips with the length of N+1 and the judgment threshold Th as specified in the specification. Frequency spectrum detection is carried out from the phase angle of the signal, under the low signal to noise ratio condition, changes of the signal phases are more obvious than the amplitude, and therefore under the low signal to noise ratio condition, the detection performance is better, and the stability is higher. The invention further discloses a device for detecting the frequency spectrum based on the adjacent phase differences.