The　photoreduction　of　the　CO2　reaction　is　a　potential　technique　for　converting　solar　energy　to　fuel　at　room　temperature,　which　speeds　up　the　recycling　and　conversion　of　carbon　compounds.　Based　on　a　highly　active　photocatalyst,　however,　disentangling　the　chemical　environments　of　surface　structures　on　the　selectivity　of　the　product　at　the　atomic　scale　is　challenging.　Herein,　we　have　explored　a　sulfur-assisted　heat　treatment　strategy　to　induce　the　reconstruction　from　surface-ordered　line　defects　to　polygonal　tungsten　line　defects,　changing　the　main　product　from　CH4　(8.2　mu　mol　h(-1),　5　mg)　to　CO　(13.0　mu　mol　h(-1),　5　mg)　without　any　additive　sacrificial　agents.　The　experimental　results　reveal　that　the　active　sites　are　the　surface　terminations　of　the　hexagonal-tungsten　line　defect,　where　the　in-plane-neighboring　W　atoms　can　break　the　C-O　bonds　inside　the　*COOH　intermediates,　thereby　promoting　the　desorption　of　CO　gas.