The　existing　fireproof　coating　on　thick　steel　structures　has　many　drawbacks,　including　its　lack　of　environmental　protection,　susceptibility　to　detachment,　prolonged　drying　duration,　and　intricate　building　procedures.　In　this　study,　magnesium　potassium　phosphate　cement　(MKPC)　was　selected　for　the　development　of　inorganic　fireproofing　coatings,　considering　that　it　has　better　adhesion,　fast　hardening　speed,　and　heat　resistance　compared　to　other　cement-based　materials.　P/M　(the　mass　ratio　of　dipotassium　hydrogen　phosphate　to　magnesium　oxide)　is　the　most　important　factor　affecting　the　performance　of　MKPC,　which　indicates　the　ratio　of　the　acid　and　base　components　of　the　system.　When　P/M　changed,　so　did　the　content　of　hydration　products　(MKP).　The　experimental　results　demonstrate　a　direct　correlation　between　the　quantity　of　MKP　and　the　performance　of　the　coating.　Consequently,　the　bonding　and　fire　resistance　mechanisms　of　MKPC　coatings　were　investigated　by　studying　the　effect　patterns　of　different　P/M　on　the　properties　(bond　strength,　fire　resistance　limit,　dry　density,　compressive　strength)　of　MKPC　fireproofing　coatings　in　combination　with　microscopic　tests　such　as　SEM,　TG-DSC,　and　MIP.　©　2025　The　Chinese　Institute　of　Engineers.