Phosphorus　recovery　from　sewage　sludge　is　necessary　to　promote　the　sustainable　recovery　of　agricultural　fertilizer　products　and　prevent　the　negative　environmental　problems.　In　this　study,　an　innovation　procedure　of　FeCl3-assisted　sewage　sludge　hydrothermal　carbonization　(HTC)　treatment　for　selective　elution　of　apatite　phosphorus　(AP)　has　been　developed　to　recover　phosphorus　as　K-struvite.　AP　of　above　88%　was　eluted　from　the　sludge　solid　phase　at　pH　of　2.5,　and　the　dissolved　phosphate　from　AP　was　mainly　fixed　by　FeCl3.　The　transformation　of　phosphorus　fractions　under　different　HTC　temperature　(200-260　degrees　C)　and　time　(0.5-4　h)　with　or　without　FeCl3　were　subsequently　investigated.　Phosphorus-31　nuclear　magnetic　resonance　(P-31　NMR)　results　showed　that　prolonging　HTC　time　and　increasing　HTC　temperature　could　disintegrate　organic　phosphorus　(OP),　while　higher　HTC　temperature　was　effective　for　decomposition　of　pyrophosphate　(Pyro-P).　The　content　of　orthophosphate　(Ortho-P)　in　hydrochar　accounted　for　above　95%　of　total　phosphorus　(TP)　under　HTC　temperature　of　200　degrees　C　for　4　h　with　FeCl3.　The　phosphate　desorption　behavior　of　hydrochar　with　FeCl3　treated　was　well　described　by　Pseudo-second-order　kinetic　model,　while　the　hydrochar　without　FeCl3　treated　followed　Pseudo　second-order　and　Elovich　kinetic　models.　About　96.1%　of　phosphate　was　extracted　from　the　hydrochar　under　pH　of　12.0　and　contact　time　of　120　min.　Finally,　about　92.6%　of　TP　in　sewage　sludge　was　recovered　as　K-struvite　to　alleviate　the　depletion　of　phosphorus　resource.