Effective　synthesis　and　application　of　single-atom　catalysts　on　supports　lacking　enough　defects　remain　a　significant　challenge　in　environmental　catalysis.　Herein,　we　present　a　universal　defect-enrichment　strategy　to　increase　the　surface　defects　of　CeO2-based　supports　through　H-2　reduction　pretreatment.　The　Pt　catalysts　supported　by　defective　CeO2-based　supports,　including　CeO2,　CeZrOx,　and　CeO2/Al2O3　(CA),　exhibit　much　higher　Pt　dispersion　and　CO　oxidation　activity　upon　reduction　activation　compared　to　their　counterpart　catalysts　without　defect　enrichment.　Specifically,　Pt　is　present　as　embedded　single　atoms　on　the　CA　support　with　enriched　surface　defects　(CA-HD)　based　on　which　the　highly　active　catalyst　showing　embedded　Pt　clusters　(Pt-C)　with　the　bottom　layer　of　Pt　atoms　substituting　the　Ce　cations　in　the　CeO2　surface　lattice　can　be　obtained　through　reduction　activation.　Embedded　Pt-C　can　better　facilitate　CO　adsorption　and　promote　O-2　activation　at　Pt-C-CeO2　interfaces,　thereby　contributing　to　the　superior　low-temperature　CO　oxidation　activity　of　the　Pt/CA-HD　catalyst　after　activation.