Anaerobic　digestion　with　thermal　hydrolysis　pretreatment　(THP),　also　called　advanced　anaerobic　digestion　(AAD),　is　a　mainstream　technology　for　sludge　treatment.　AAD　changes　sludge,　it　can　degrade　extracellular　polymeric　substances　(EPS),　release　EPS　from　the　sludge,　and　alter　the　particle　size　distribution.　We　synthesized　PFS-　PDMDAAC　from　the　inorganic　coagulant　polyferric　sulfate　(PFS)　and　the　organic　coagulant　polymer　polydimethyldiallylammonium　chloride　(PDMDAAC)　in　various　PFS:　PDMDAAC　weight　ratios.　We　investigated　the　effects　of　PFS-　PDMDAAC　pretreatment　on　AAD　sludge　dewaterability,　and　developed　an　explanation　for　them.　Capillary　suction　time　(CST)　was　used　as　a　measure　of　sludge　dewaterability.　Dissolved　organic　matter,　the　three-dimensional　excitation　emission　matrix,　particle　size　(d0.5),　zeta　potential,　and　sludge　microstructure　were　observed　in　order　to　explain　changes　in　sludge　dewaterability　that　resulted　from　different　compositions　and　dosages　of　coagulants.　Treatment　with　PFS　alone　gave　no　significant　improvement　in　sludge　dewaterability.　PDMDAAC　used　alone　greatly　improved　sludge　dewaterability.　Synthesized　PFS-PDMDAAC　which　had　a　relatively　high　proportion　of　PDMDAAC　by　weight　performed　similarly　to　PDMDAAC.　PFSPDMDAAC　synthesized　in　the　ratio　(PDF:　PDMDAAC)　1:　5　by　weight　provided　good　dewaterability.　The　dosage　can　be　reduced　by　16.7%　of　the　dosage　for　conditioning　by　PDMDAAC　alone.