xPtSSG　(xPtSmCoO3/SBA-15/GO,　x　=　0.37,　0.83　and　0.88)　was　prepared　via　deposition-precipitation　and　polyvinyl　alcohol-protected　reduction　method,　and　the　catalytic　activity　was　evaluated　by　the　CO　conversion　of　water　gas　shift　(WGS).　The　crystal　structure　and　physicochemical　properties　of　the　catalysts　were　evaluated　by　numerous　techniques.　Pt　species　were　present　as　single　atoms　or/and　nanoparticles　over　xPtSSG　samples.　Graphene　oxide　(GO)　as　an　electron　transfer　bridge　could　significantly　strengthen　the　strong　metal-support　interaction　(SMSI)　between　Pt　and　SSG,　thus　significantly　enhancing　catalytic　activity.　Among　all　the　samples,　the　lower　Pt-loading　single　atom　Pt　0.37PtSSG　sample　had　the　highest　specific　rate　(0.84　molCO　gPt　-1)　and　TOF　(4.5　x　10-2　s-1　at　250　degrees　C),　which　may　be　due　to　the　higher　oxidation　state　of　Pt　species　(3.39)　via　Co-PtOx,　high　Oads/　Olat　molar　ratio　and　good　low-temperature　reducibility.　The　DRIFTS　demonstrates　that　CO2　was　produced　by　the　redox　mechanism　between　CO　and　oxygen　species　over　single　atom　Pt　0.37PtSSG　catalyst.　However,　CO　reacted　with　OH　by　associative　mechanism　to　produce　formate　or　carboxylate　intermediates　over　the　nano-Pt　0.88PtSSG　sample.　By　DFT　calculation　of　CO　adsorption　over　the　(02　0)　crystal　plane　of　perovskite,　the　adsorption　energy　on　Pt　single　atoms　was　significantly　lower　than　that　of　Pt　nanoparticles,　thus　confirming　the　catalytic　activity　of　Pt　single　atoms　was　higher　than　that　of　Pt　nanoparticles.　This　work　provides　an　effective　approach　to　designing　a　high-performance　catalyst　for　water　gas　shift　reaction.