In　this　paper,　we　prepare　several　GexSb20Se80-x　glasses　(x　=　5　mol%,　10　mol%,　15　mol%,　17.5　mol%,　20　mol%,　and　25　mol%),　and　measure　their　Raman　and　X-ray　photoelectron　spectra　(Ge　3d,　Sb　4d,　and　Se　3d)　in　order　to　understand　the　evolution　of　the　glass　structure　with　chemical　composition.　We　further　decompose　the　spectra　into　different　structural　units　according　to　the　assignments　of　these　structural　units　in　the　previous　literature.　It　is　found　that　the　structural　units　of　Se-Se-Se　trimers　exist　in　the　Se-rich　glasses,　but　the　number　of　the　structural　units　of　trimers　decreases　rapidly　with　the　increase　of　Ge　concentration　and　finally　becomes　zero　in　Ge15Sb20Se65　glass.　With　the　increase　of　Ge　concentration,　the　quantity　of　GeSe4/2　tetrahedral　structures　increases,　but　the　number　of　SbSe3/2　pyramidal　structures　remains　almost　unchanged　in　the　Se-rich　glasses.　On　the　other　hand,　the　numbers　of　Ge-Ge　and　Sb-Sb　homopolar　bonds　increase　with　the　increase　of　Ge　concentration,　but　those　of　the　GeSe4/2　tetrahedral　and　SbSe3/2　pyramidal　structures　decrease　in　the　Se-poor　glasses.　Moreover,　the　Se-Se　homopolar　bonds　exist　in　all　the　glasses,　and　they　cannot　be　completely　suppressed.　When　the　composition　is　close　to　stochiometric　value,　the　glass　is　dominated　by　heteropolar　Ge-Se　and　Sb-Se　bonds,　but　has　negligible　quantities　of　Ge-Ge,　Sb-Sb　and　Se-Se　homopolar　bonds.　The　transition　threshold,　rather　than　the　transition　predicted　by　the　topological　constraint　model,　occurs　at　the　chemically　stoichiometric　glasses.　This　suggests　that　chemical　order,　rather　than　topological　order,　is　a　main　factor　in　determining　structures　and　physical　properties　of　Ge-Sb-Se　glasses.