The　magnesium　phosphate　cement　(MPC)　is　a　carbon-free　cementitious　material,　widely　used　in　solidification　of　nuclear　waste,　heavy　metals,　and　repair　and　reinforcement.　The　magnesium　potassium　phosphate　hexahydrate　(MgKPO4　center　dot　6H(2)O,　MKP)　is　the　main　hydration　product　of　MPC,　seriously　affecting　the　mechanical　properties　of　the　MPC.　Therefore,　this　paper　presented　an　experimental-computational　approach　to　investigate　the　mechanical　properties　of　the　MKP　through　nanoindentation　with　X-ray　Computed　Tomography　(X-CT)　technique　and　finite　element　analysis.　Firstly,　the　micro-mechanical　properties　and　structural　distribution　characteristics　of　the　MKP　were　tested　based　on　the　nanoindentation　and　the　X-CT　technique,　respectively.　Then,　the　3D　structure　grid　model　of　the　MKP　was　obtained　based　on　X-CT　data,　imported　into　the　ABAQUS　software　for　the　finite　element　simulation.　Besides,　considering　the　effect　of　porosity　and　pore　distribution　on　the　damage,　the　modified　MKP　constitutive　relation　was　proposed　and　input　into　the　X-CT　nanoindentation　model　and　the　RAP　nanoindentation　model,　respectively.　It　was　found　that　those　two　models　can　effectively　describe　the　mechanical　and　deformation　characteristics　of　the　MKP,　which　verified　the　correctness　of　the　modified　constitutive　relationship　of　MKP.　Finally,　the　influence　of　pore　distribution　on　the　nanoindentation　results　was　predicted　based　on　the　RAP　nanoindentation　model.