The present invention provides a fiber optic distributed sensing monitoring system, and belongs to the technical field of the fiber optic distributed sensing technology. The system comprises a signal light generating device, a first optical coupler, a sensing optical fiber, a light beam splitter, a first polarization controller, a second polarization controller, a first interference modulation device, a second interference modulation device and a demodulation device. A first linearly polarized light outputted by the first polarization controller is subjected to interference modulating by the first interference modulation device. A second linearly polarized light outputted by the second polarization controller is subjected to interference modulating by the second interference modulation device. Furthermore, a first interference signal outputted by the first interference modulation device and a second interference signal outputted by the second interference modulation device are demodulated, so that corresponding sensing signals are obtained. In this way, the losing of sensing signals is avoided as much as possible. Meanwhile, the signal-to-noise ratio of the fiber optic distributed sensing monitoring system is effectively improved.