A systematic investigation of the optical and structural properties of chalcogenide glasses in Ge-Sn-Se ternary system is presented. We have found a threshold behavior of optical property, namely, existence of transitional composition of the Ge-Sn-Se glasses, with progressive replacement of Se by Sn. Calculation of mean coordination number indicates that the transition-like feature of optical property is associated with the evolution of chemical ordering of the Ge-Sn-Se network. Analysis of Raman spectra of the glasses explains that the interaction between Se-Se bonds, Sn(Se-1/2)(4) tetrahedra, and Sn-Sn homopolar bonds is the origination of such optical phenomenon.