The invention provides a distributed fiber-optic gas sensor based on suspension core optic fibers, comprising an optical source, an optical time domain refectometer, a coupled connector and an optical fiber, wherein the optical fiber comprises standard optical fibers and the suspension core optic fibers coupled with the standard optical fibers; a round or D-shaped one-dimensional pore canal along the axial direction of the optical fiber is arranged between a fiber core of the suspension core optic fibers and a cladding; the refractive index of the fiber core is higher than that of the cladding; the fiber core is suspended on the inner wall of the one-dimensional pore canal by clinging or is partially embedded in the cladding; the cladding in the whole length range of the suspension core optic fibers is provided with an exposed structure. The invention can realize modulation of the optical wave signals and remarkably simplify the structure design and the volume of the sensor. The sensor can arrange long-distance sensing units in the mines, gas pipelines and other places, quickly respond to gas leakage and accurately judge the leak points.