To　find　the　optical　properties　of　Cu2ZnSnS4　(CZTS)　absorber　in　two　crystal　structures　(kesterite　and　stannite)　which　are　key　factors　determining　solar　cell　performance　and　are　based　on　the　electronic　structures,　a　systematical　calculation　of　electronic　and　optical　properties　were　calculated　using　density　functional　theory.　The　results　suggested　that　the　optical　properties　of　CZTS　had　a　rather　weak　dependence　on　the　(Cu,　Zn)　cation　ordering.　Kesterite　and　stannite　CZTS　both　suited　for　photovoltaics　with　large　light　absorption　coefficient　(＞　104　cm-1)　in　the　visible　light　region　that　is　the　most　important　part　for　photovoltaics,　and　kesterite　CZTS　had　larger　light　absorption　than　stannite　CZTS　exhibiting　a　more　obvious　advantage.　In　the　visible　light　region　the　reflectivity　of　CZTS　was　lower　than　that　of　silicon,　the　absorber　material　used　most　widely,　which　might　be　in　favor　of　light　absorption　and　cell　efficiency.　Ground-state　structure,　electronic　transitions　relevant　to　solar　light　absorption,　static　dielectric　constant　and　plasma　frequency　were　also　investigated.　©　(2015)　Trans　Tech　Publications,　Switzerland.