The dispersion functioning mechanism of low-dispersion halides on chalcogenide glasses is studied on the influence of glass composition optimizing, refractive index adjusting and zero-dispersion wavelength shifting, with the help of Ge-Ga-Se-CsI chalcohalide glass preparation. The physical and infrared optical properties of the glasses were tested by differential scanning calorimetry, infrared ellipsometer and infrared spectrometer. The purification process and glass composition to the glass formation and their optical properties were studied detailedly. The material dispersion curves of the two glass samples were calculated based on the measured data of refractive index. The experimental results show that the transmission range of the glasses is from visible to far infrared (0.55~18 μm); With the content of CsI increasing, the zero-dispersion wavelength of material decreases, in the value of 3.5 μm and 1.5 μm, corresponding to 20% CsI- and 40% CsI-chalcohalide glass, respectively. At the same time, the thermal stability of the two glasses is enough high, which is favorable for the preparation of low-dispersion mid-infrared fiber. Combined with effective glass purification method and high-temperature polymer-coating protection, a single refractive index chalcohalide glass fiber with a minimum loss of 8.2 dB/m was obtained.