The invention discloses a long-distance small displacement detecting method based on microwave signals. A microwave transmitter is fixed to a measured target object and moves along with the measured target object. The microwave transmitter emits a microwave signal to bypass a metal circular barrier, and then a microwave signal receiving device performs microwave detection. The microwave signal receiving device includes first, second and third receiving antennas and a receiving detecting circuit. The second receiving antenna is placed at a determined Arago point formed by the diffraction of themicrowave signal bypassing the metal circular barrier. The signal amplitudes and the phase differences of the receiving antennas are compared to obtain the small displacement of a microwave source less than the wavelength scale. The signal amplitudes, phases and frequencies of the receiving antennas are compared to obtain the amplitude and the frequency of the micro vibration of the long-range microwave source smaller than the wavelength scale. The method is suitable on occasions where an optical method cannot be used, is low in cost, high in measurement sensitivity, simple in system deployment, and good in applicability.