wt% Tm³⁺-doped 72GeS₂-18Ga₂S₃-10CsI (GGSI) chalcohalide g lasses are synthesized by vacuumed melting-quenching technique and the properties of glasses including refractive index,absorption s pectrum,mid-infrared (IR) emission spectrum under 800nm exicitation are measured.The optical parameters,such as predicted spontaneous tr ansition probability (A),branching ratio (β),radiative lifetime (τrad), absorption cross-section (σa) and emission cross -section (σe),by means of Judd-Ofelt and Fuchba uer-Ladenburg theories are calculated.Based on the rate equations and power pro pagation equations,the Tm³⁺-doped GG SI glass fiber amplifier modeling is analyzed and the numerical simulations on w avelength of 3.73μm mid-infrared gain characteristics versus the fiber lengt h,pump power and signal power are discussed in this paper.It is shown that the T m3＋-doped chalcohalide glass fiber exhibits a higher signal gain and br oad mid-infrared gain spectrum:its maximum gain of small signal and the gain wi dth at 20dB reach 30dB and 180nm,respectively for pump power of 1000mW.Simulation results also show that there exist the most suitable p u mp power and fiber length while the amplifier has the maximum signal gain. Theoretical study ind icates that the Tm³⁺-doped GGSI chalcohalide glass fiber is a suitable ga in medium which can be applied to amplifiers in the mid-infrared wavelength reg ion.