The　hydration　rate,　microstructure,　mechanical　properties　and　durability　of　Magnesium　phosphate　cement　(MPC)　prepared　by　different　kinds　of　phosphates　are　quite　different.　These　differences　in　macroscopic　properties　are　essentially　determined　by　microscopic　chemical　reactions.　Therefore,　in　this　paper,　the　adsorption　mechanism　of　MgO　interface　to　water　and　ions　in　the　initial　hydration　process　of　MPC　and　the　hydration　structure　of　different　ions　were　discussed　at　the　molecular　level.　Herein,　the　structure　and　dynamics　properties　of　water,　NH4+,　Na+,　K+　and　Cl　ions　at　MgO　interface　were　analyzed　by　molecular　dynamics　method.　The　results　show　that　the　water　molecules　near　the　MgO　interface　can　be　connected　to　the　matrix　oxygen　through　hydrogen　bonding　and　have　a　Coulomb　interaction　with　the　Mg　on　the　interface.　Therefore,　the　water　molecules　accumulate　and　stratify　at　the　interface　and　the　density　distribution　curve　of　water　molecules　forms　a　peak　near　the　interface.　This　explains　the　stage　of　MgO　adsorption　of　water　molecules　during　the　initial　hydration　of　MPC.　Besides,　a　large　amount　of　ammonium　ion,　sodium　ion　and　potassium　ion　are　adsorbed　on　the　MgO　surface,　and　the　cation　density　distribution　curve　also　forms　a　peak　near　the　interface.　In　addition,　the　radius　of　sodium　ion　is　smaller　and　the　Na-Os　bond　is　stronger　than　that　of　NH4+　and　K+　(Os　represents　the　oxygen　atom　in　MgO).　Hence,　the　number　of　sodium　ions　adsorbed　to　the　interface　is　the　largest,　the　radial　distribution　function　(RDF)　of　Na-Os　forms　a　high-　strength　and　sharp　peak,　The　Os　coordination　number　of　Na+　is　more　than　that　of　NH4+　and　K+.　This　also　explains　the　experimental　phenomenon　that　sodium　magnesium　phosphate　cement　has　a　faster　hydration　rate　and　shorter　setting　time　than　ammonium　magnesium　phosphate　cement　and　potassium　magnesium　phosphate　cement.　Due　to　the　adsorption　of　the　interface,　the　mean　square　displacement　of　cations　has　decreased　to　some　extent　compared　with　that　in　the　corresponding　pure　solution　models.　This　study　provides　a　basic　understanding　of　the　initial　hydration　mechanism　of　MPC　at　the　molecular　level.　(C)　2020　Published　by　Elsevier　Ltd.