The　effect　of　the　type　and　content　of　multi-wall　carbon　nanotubes　(MWCNTs)　on　the　damping　performance　of　cement　mortar　is　studied　in　this　paper.　The　pristine　MWCNTs　(P-CNT)　and　the　functionalized　MWCNTs　(F-CNT)　grafted　with　COOH　were　used　in　the　experiment.　The　content　of　MWCNTs　was　0.05wt%　and　0.1wt%　of　cement.　The　flexural/compressive　strength　and　loss　factor　of　CNT-mortar　composites　were　measured.　The　experimental　results　show　that　MWCNTs　can　significantly　enhance　the　flexural　strength　and　loss　factor,　and　the　values　increased　with　the　increase　of　CNTs　content.　The　effect　F-CNT　was　better　than　P-CNT　when　the　MWCNTs　content　was　the　same　due　to　the　presence　of　COOH.　The　mechanism　of　MWCNTs　reinforced　mortar　damping　performance　was　analyzed　by　a　variety　of　micro　test　techniques.　The　test　results　of　X-ray　diffraction,　X-ray　photoelectron　spectroscopy,　Fourier　transform　infrared　spectroscopy　and　thermogravimetry　showed　that　MWCNTs　did　not　change　the　compositions　of　mortar,　but　improved　the　polymerization　degree　of　gel　and　the　degree　of　hydration　of　cement.　The　results　of　mercury　intrusion　porosimetry,　N-2　adsorption　and　backscattered　scanning　electron　microscopy　showed　that　MWCNTs　effectively　reduced　the　porosity　and　interfacial　transition　zone　thickness　of　mortar.　Transmission　electron　microscope　results　showed　that　the　energy　dissipation　capacity　of　mortar　is　increased　due　to　the　bridging　effect　of　MWCNTs.