The invention discloses a laser frequency shift detecting method and device with a dual-cavity F-P interferometer which is formed on the basis of polarization maintaining optical fibers. The device comprises a laser device, an acoustic optical modulator (AOM), an erbium-doped optical fiber amplifier (EDFA), quarter-wave plates, a collimator, a telescope, a first polarization maintaining optical fiber, a first circulator, a first narrow-band fiber bragg grating (FBG), a polarization controller (PC), an optical fiber F-P interferometer, an F-P interferometer controller, a polarization beam splitter (PBS), a first single photon counting module (SPCM), a second SPCM, a second polarization maintaining optical fiber, a second circulator, a second narrow-band FBG, a third SPCM and an acquisition card. According to the laser frequency shift detecting method and device with the dual-cavity F-P interferometer which is formed on the basis of the polarization maintaining optical fibers, a laser radar fiber integrated single-emission double-receiving light path is developed, two receiving optical fibers are spliced in the same cladding to form a dual D involution optical fiber, separation of energy detection and frequency shift detection is achieved, the signal to noise ratio of the frequency shift detection is increased, a dual-edge detection technology can be successfully achieved only by the single-channel F-P interferometer, the energy utilization ratio is high, and the method is simple.