In　a　CIGS　thin　film　solar　cell,　the　buffer　layer　is　interposed　between　the　absorber　layer　and　the　window　layer,　which　plays　an　important　role　in　interface　electricity.　CdS　is　often　used　as　a　buffer　layer　in　CIGS　cells.　Beside　the　toxicity　of　Cd,　the　main　drawback　of　CdS　is　its　relatively　narrow　band　gap　(2.4　eV),　which　can　lead　to　the　current　loss　due　to　parasitic　absorption.　In　order　to　reduce　the　use　of　CdS,　we　try　other　buffer　layers　instead　of　CdS　and　optimize　buffer　layer　structure.　Numerical　simulation　has　been　used　to　explore　the　effect　of　different　buffer　layer　materials　(CdS　and　ZnSe)　on　the　performance　of　CuInGaSe2　solar　cells　with　SCAPS-1D　software.　The　main　photovoltaic　parameters　of　the　analog　device:　open　circuit　voltage,　short　circuit　current　density,　fill　factor　and　conversion　efficiency　(eta)　were　compared　and　analyzed.　The　results　show　that　different　buffer　materials　and　thickness　have　great　influence　on　the　performance　of　the　cell.　In　this　simulation,　CdS　buffer　layer　was　replaced　by　ZnSe　material,　which　has　a　wider　band　gap.　However,　the　efficiency　of　this　kind　of　cell　is　lower　than　that　of　CIGS　device　with　CdS　buffer　layer　because　of　the　bad　energy　band　alignment.　In　order　to　improve　the　short-wave　absorption　and　the　efficiency　of　CIGS　cell,　we　simulated　a　novel　CdS/ZnSe　double　buffer　layer　structure.　The　efficiency　of　the　optimized　cell　with　double　buffer　layer　increases　from　18.47%　(conventional　cell　with　the　same　CdS　buffer　layer　thickness)　to　19.01%.