We demonstrate a distributed fiber optics disturbance sensing system based on a dual-Sagnac interferometer that uses one broadband light source and works at the same wavelength. This proposed sensing system is able to reduce the coherent noise and avoid the influence of polarization crosstalk effectively. Experimental results show that, for the presented prototype system with the fiber loop of 1.3 Km, when the sampling rate is set as 32.8 kHz, the maximum detectable frequency reaches the system theoretical limit of 8.18 kHz, and the spatial resolution is less than 15 m with a frequency range of 50-4000 Hz.