Defect　engineering　has　been　widely　applied　in　semiconductors　to　improve　photocatalytic　properties　by　altering　the　surface　structures.　This　study　is　about　the　transformation　of　inactive　WO　3　nanosheets　to　a　highly　effective　CO　2　-　to　-　CH　4　conversion　photocatalyst　by　introducing　surface　-　ordered　defects　in　abundance.　The　nonstoichiometric　WO　3　-　x　samples　were　examined　by　using　aberration　-　corrected　electron　microscopy.　Results　unveil　abundant　surface　-　ordered　terminations　derived　from　the　periodic　{013}　stacking　faults　with　a　defect　density　of　20.2%.　The　{002}　surface　-　ordered　line　defects　are　the　active　sites　for　fixation　CO　2　,　transforming　the　inactive　WO　3　nanosheets　into　a　highly　active　catalyst　(CH　4　:　O　2　=　8.2:　16.7　mu　mol　h　-1　).　We　believe　that　the　formation　of　the　W　-　O　-　C　-　W　-　O　species　is　a　critical　step　in　the　catalytic　pathways.　This　work　provides　an　atomic　-　level　comprehension　of　the　structural　defects　of　catalysts　for　activating　small　molecules.