Thermal-electricity　conversion　is　one　of　the　most　promising　routes　to　harvest　heat　and　convert　it　as　easily　storable　and　deliverable　electric　energy.　Significant　progress　has　been　made　since　the　discovery　of　Seebeck　effect　in　1821,　particularly,　the　figure　of　merit　zT　approached　a　record　high　value　of　2.6　in　2014.　However,　for　thermoelectric　devices,　high　average　zT　values　(zT(ave))　over　the　operating　temperature　range　is　more　important　as　it　is　directly　related　to　the　conversion　efficiency　(eta).　Approaching　highly　stable　and　repeatable　ultra-high　zT(ave)　for　Te-free　materials　has　been　historically　challenging　over　the　past　century　though　exciting　progress　with　zT(ave)　well　above　1.10　was　made　recently.　Here,　through　synergistic　band　engineering　strategy　for　single　crystalline　SnSe,　we　report　a　series　of　record　high　zT(ave)　over　a　wide　temperature　range,　approaching　similar　to　1.60　in　the　range　from　300　K　to　923　K　in　Na-doped　SnSe0.9S0.1　solid　solution　single　crystals,　with　the　maximum　zT　of　2.3　at　773　K.　These　ultra-high　thermoelectric　performance　derive　from　the　new　multiple　valence　band　extrema　near　the　band　edges　in　SnSe0.9S0.1　and　the　shift　of　Fermi　level　towards　the　multi-valley　bands　through　Na　doping　which　introduce　additional　carrier　pockets　to　attend　electrical　transport.　These　effects　result　in　an　optimized　ultrahigh　power　factor　exceeding　4.0　mW　m(-1)　K-2　in　Sn0.97Na0.03Se0.9S0.1　single　crystals.　Combined　with　the　extremely　lowered　thermal　conductivity　attributed　from　the　intrinsic　anhar-monicity　and　point　defect　phonon　scattering,　the　series　of　ultra-high　zT(ave)　and　a　record　high　calculated　conversion　efficiency　of　21%　over　a　wide　temperature　range　are　approached.