A low-temperature drawing-tower is designed and established to fabricate gradually tapered capillary by using polycarbonate perform.With inner-coatings of silver（Ag）and silver iodide（AgI）layers

flexible gradually tapered hollow waveguide is made and low loss property is obtained at the wavelength of 3.3μm.Transmission characteristics of the waveguide are investigated theoretically and experimentally.The influences of waveguide length

bending radius

and incident direction on the system property are investigated by experiment of methane gas detection.The results show that the coupling efficiency increases when the light incidence from the large end

and the detection limit and the sensitivity improves.The system has higher saturated absorbance when the light incidence from the small end.