The invention provides a weak reflection-FIZEAU sensing device comprising a sensing end used for reflecting multiple scanning laser with different wavelengths and a demodulating end used for demodulating optical signals reflected by the sensing end to obtain a measurement result, wherein the sensing end comprises an optical circulator and a polarization maintaining optical fiber, weak reflection FBG-FIZEAU optical fiber resonant cavities in the same as the scanning laser wavelengths are arranged in each segment of polarization maintaining optical fiber, and each segment of polarization maintaining optical fiber is correspondingly provided with a serially connected optical circulator; and the demodulating end comprises a multi-wavelength scanning laser, a polarization controller, a linear polarizer, an optical switch, a wavelength division multiplexer, a photoelectric detector and a signal analysis module. Compared with the prior art, high-precision demodulation is realized by measuring the stripe contrast of sensing signals, the requirements on the performance of the wavelength scanning laser are not high, and a reference sensor is omitted, so that the system is simple, and the cost is low.