Silica　fume　(SF)　is　commonly　used　in　producing　magnesium　potassium　phosphate　cement　(MPC)　and　magnesium　silicate　hydrate　cement　(MSHC).　However,　its　roles　in　magnesium　cement　would　differ　from　each　other　when　mono　hydrogen　phosphate　was　involved.　This　paper　aims　to　find　optimized　compositions　in　MgO-K2HPO4　DKPSF　system　with　comprehensive　considerations　of　the　micro　and　macro　performances.　Ternary　contour　maps　were　designed　to　determine　the　optimized　proportions　of　MgO,　DKP　and　SF.　The　hydration　reaction　mechanism　was　analyzed　with　a　variety　of　techniques　including　XRD,　SEM,　TG-DTG　and　NMR.　Magnesium　cement　containing　60-75　%　dead-burnt　MgO,　10-25　%　DKP　and　12.5-25　%　SF　exhibited　excellent　compressive　strength　and　volume　stability.　K-struvite　and　M-S-H　were　confirmed　to　promote　the　hydration　and　hardening　performance　of　the　blended　MgO-DKP-SF　system　with　optimized　proportions.　An　excess　of　soluble　K+　from　DKP　may　precipitate　as　KOH　and　then　dissolute　in　solution,　increasing　pH　and　release　of　Si　from　SF.