Er3+-doped 80GeS2-10In2S3-10CsI(mol%)chalcohalide glass was fabricated by melt-quenching technique. The thermal stability, Raman spectra, absorption spectra, upconversion emission spectra of glass samples were measured, and upconversion mechanisms of Er3+ in the glass were analyzed. The intensity parameters(Ωt,t=2,4,6), spontaneous transition probabilities(Α), fluorescence branching ratios(β), and radiative lifetimes(τrad) were calculated by using the Judd-Ofelt theory. Under 980 nm diode laser excitation, intense emission bands centered at 526 nm and 549 nm corresponding to the transitions of 2H11/2→4I15/2 and 4S3/2→4I15/2 , respectively, were observed for the first time in this glass, and intensity of 549 nm green light is more stronger. For 549 nm emission band, the upconversion fluorescence lifetime is 0.34 ms, and the quantum efficiency is 69%. The dependence of visible emission intensities upon excitation intensity was examined. A plot of logIUP vs logIIR yields two fitted lines with slope 1.71 and 2.03, respectively, which indicates a two-photon process for green emission. Results suggest that Er3+-doped 80GeS2-10In2S3-10CsI chalcohalide glass may be a potential host material for upconversion green lasers.