With the development of infrared optical fiber technology, it is urgent to develop an infrared low loss chalcogenide optical fibers with perfect-structure and high nonlinearity. In this paper, the two kinds of glass samples of As40Se58Te2 and As40Se60 are prepared by the traditional vacuum melt-quenching method and dynamic distillation purification process. Then we obtain a fine-structured chalcogenide optical fiber prefabricated rod prepared by two multi-step extrusion method. After that, the preform is drawn into a low loss step type single-mode chalcogenides glasses fiber under the protection of polyether sulfone (PES) polymer. The results show that the distillation process can effectively remove most of the impurities in the chalcogenide glasses. 2% mole percent of Se is replaced by Te, which can effectively achieve a small numerical aperture (NA) and single-mode transmission characteristics. The single-mode chalcogenides fiber loss test is measured by the truncation method with a Fourier transform infrared spectroscopy spectrometer. The minimum loss of this fiber can be reduced to 1.66 dB/m at 6.06 μm and these glasses working band is from 2.5 to 12 μm. The output of a supercontinuum spectrum covering 1.5-13.2 μm (40 dB bandwidth) is obtained with an optical parametric amplifier (OPA) as the pump source. The fiber has good mid-far infrared transmission performance and extremely high optical nonlinearity.