The　effect　of　MWCNTs　on　the　creep　properties　of　C-S-H　was　investigated　based　on　nanoindentation　test,　and　the　detailed　mechanism　analysis　was　carried　out　by　atomic　force　microscope　(AFM)　and　nuclear　magnetic　resonance　(NMR)in　this　paper.　The　Portland　cement　and　multi-walled　carbon　nanotubes　(MWCNTs)　grafted　with　COOH　were　used　in　the　experiments.　The　water　to　cement　ratio　was　0.3　and　the　content　of　MWCNTs　was　0.05　wt%　of　cement.　The　results　of　nanoindentation　test　showed　that　the　creep　modulus　of　low　density　C-S-H　and　high　density　C-S-H　of　the　sample　doped　with　MWCNTs　(CC)　was　39.2%　and　21%　higher　than　that　of　the　control　sample　(PC),　respectively,　indicating　the　creep　deformation　of　C-S-H　was　significantly　reduced　by　MWCNTs.　Foil　shape　in　CC　was　observed,　and　the　elastic　modulus　and　Hamaker　constant　of　C-S-H　at　submicron-scale　were　higher　than　those　of　PC　measured　by　AFM.　The　results　of　mercury　intrusion　porosimetry　test　showed　that　the　porosity　and　most　probable　pore　size　of　CC　decreased　compared　with　PC.　The　mean　chain　length　increased　for　CC　measured　by　29Si　NMR.　And　the　low-filed　1H　NMR　results　showed　that　the　proportion　of　interlayer　water　was　almost　not　changed　with　the　incorporation　of　MWCNTs,　suggesting　that　the　influence　of　interlayer　water　on　C-S-H　creep　properties　can　be　ignored.　Based　on　the　experimental　results,　the　mechanism　was　proposed　to　explain　the　decrease　of　C-S-H　creep　deformation　by　MWCNTs:　(1)　foil　shape　C-S-H　was　not　easy　to　slip;　(2)　less　free　volume　available　for　globules　to　slip;(3)　the　stronger　force　existed　between　globules;　(4)　the　network　structure　was　formed　in　C-S-H　due　to　the　presence　of　MWCNTs　and　the　elastic　modulus　of　C-S-H　increased,　resulting　in　more　resistance　for　deformation.