Graphene　oxide　(GO)　is　an　excellent　nano　reinforcing　material.　This　paper　presents　the　effect　of　GO　addition　on　the　hydration,　microstructure　and　mechanical　properties　of　magnesium　phosphate　cement　(MPC).　MPC　with　GO　contents　of　0.00,　0.02,　0.04,　0.06,　0.08　and　0.10　%　was　prepared.　The　functional　groups,　mechanical　properties,　phase　composition　and　reinforcement　mechanism　of　the　GO-MPC　composites　were　tested　and　analysed.　The　results　showed　that　water　adhered　to　the　GO,　which　led　to　a　decrease　in　the　fluidity　of　the　MPC　paste.　With　increasing　GO　content,　the　most　probable　pore　size　of　MPC　first　decreased　and　then　increased.　By　adding　0.04　%　GO,　the　most　probable　aperture　of　MPC　was　reduced　from　11.3　mu　m　to　0.9　mu　m.　The　proper　addition　of　GO　could　refine　the　pore　size,　densify　the　microstructure　and　improve　the　mechanical　properties　of　MPC.　An　appropriate　dosage　of　GO　promoted　the　hydration　of　MPC,　resulting　in　more　hydration　products,　including　potassium　magnesium　phosphate　hexahydrate　(MKP),　better　growth　of　MKP　with　higher　crystallinity.