The present disclosure provides a dual-wavelength distributed optical fiber acoustic sensing system including: a first narrow linewidth laser, a second narrow linewidth laser, a primary main coupler,an optical isolator, a modulator, an erbium doped optical fiber amplifier, a circulator, a first optical fiber grating, a second optical fiber grating, a sensing optical fiber, a wavelength division multiplexer, a first Michelson interferometer, a second Michelson interferometer, a first carrier circuit, a second carrier circuit, a first photodetector, a second photodetector, a data acquisition card, a signal processor and a pulse generator. Two phase demodulation results with different spatial resolutions but close to each other are realized by wavelength division multiplexing, and high spatial resolution distributed dynamic vibration or acoustic signal monitoring is obtained by subtracting the two phase demodulation results; since there is no need to reduce the interferometer arm lengthdifference and the pulsed light width, less noise of the system can be ensured.