A serial of chalcogenide glasses with the composition of Ge28Sb6S(66－x)Sex(x=0, 10, 20, 30, molar fraction) are prepared by the melt-quenching technique. The densities, refractive indexes, VIS-NIR transmission spectra, IR transmission spectra and Raman spectra of the samples are measured respectively. The impact of the presence of Se on the physical and optical properties of Ge-Sb-S glass system are analyzed. The Raman spectra are used to discuss the relationship between structures and properties. Results show that with increasing Se content, the densities and refractive indexes of the samples increase, and the visible and IR cut-off edges shift towards longer wavelengths. The basic structural units of the pure sulfide glass are GeS4 tetrahedra and SbS3 pyramids. With the substitution of S by Se, the sulfur-selenide-containing samples present GeS4－xSex units and Se-Se homopolar bonds both in rings and in chains.