The present invention discloses a fiber fabry-perot cavity demodulation method, a device thereof and a fiber fabry-perot interferometer. The fiber fabry-perot cavity demodulation method comprises the steps of acquiring a spectral signal of an interference fiber fabry-perot cavity; subjecting the spectral signal to first demodulation through adopting non-equally dispersed fourier transform so as to obtain a first cavity length value of the fiber fabry-perot cavity, wherein the accuracy of the first cavity length value is greater than a first threshold value and the cavity length demodulation of the fiber fabry-perot cavity is free of the half-wave hopping phenomenon when the accuracy of the first cavity length value is greater than the first threshold value; and according to the first cavity length value, subjecting the spectral signal to second demodulation so as to obtain the second cavity length value of the fiber fabry-perot cavity, wherein the accuracy of the second cavity length value of the fiber fabry-perot cavity is greater than the accuracy of the first cavity length value. According to the technical scheme of the invention, the problem in the prior art that the cavity length demodulation accuracy of the fiber fabry-perot cavity is not high can be solved. Therefore, the demodulation accuracy of the cavity length of the fiber fabry-perot cavity is improved.