In order to demonstrate the characteristics of chalcogenide glass Er3+-doped microstructured optical fiber (MOF) amplifying the mid-infrared band signal, Er3+-doped Ga5Ge20Sb10S65 chalcogenide glass is prepared with high temperature melt-quenching method. The absorption spectrum and 2.7 m band fluorescence spectrum of glass sample are measured, and the spectroscopic parameters such as radiative transition probability, radiative lifetime and 2.7 m band stimulated emission cross-section of Er3+ ion are calculated and analyzed according to the Judd-Ofelt and Futchbauer-Ladenburg theories. The 2.7 m band mid-infrared signal amplifying model of Ga5Ge20Sb10S65 chalcogenide glass Er3+-doped MOF under the excitation of 980 nm is presented, and the amplifying characteristics of 2.7 m-band mid-infrared signals for chalcogenide glass Er3+-doped MOF are investigated theoretically. The results show that the chalcogenide glass Er3+-doped MOF exhibits a higher signal gain and very broad gain spectrum: its maximal gain of small signal exceeds 40 dB and amplifying bandwidth of higher than 30 dB gain reaches about 120 nm (26962816 nm) for a 100 cm long chalcogenide glass erbium-doped MOF with a pump power of 200 mW. The theoretical studies indicate that the Ga5Ge20Sb10S65 chalcogenide glass Er3+-doped MOF is an excellent gain medium which can be applied to broadband amplifiers in the mid-infrared wavelength region.