A　hydrolysis-anoxic-oxidation　(H-A-O)　combined　system　for　enhanced　nitrogen　removal　and　waste　activated　sludge　(WAS)　reduction　within　the　process　was　designed.　This　combined　system　was　conducted　continuously,　and　domestic　wastewater　was　treated.　Influent　chemical　oxygen　demand　(COD)　and　NH4+-N　concentration　were　220-410　mg/L　and　36-58　mg/L,　and　the　ratio　of　nitrification　liquid　return　(r)　was　300%.　Experiment　results　indicate　that　domestic　wastewater　biodegradability　increases　by　60%　under　the　function　of　hydrolysis　and　acidification.　Without　external　C-source　and　alkalinity　addition,　COD,　NH4+-N　and　TN　removal　efficiency　in　this　system　reach　90%,　95%　and　74%,　where　total　nitrogen　(TN)　removal　efficiency　increases　by　12%.　When　WAS　hydrolysis　effluent　and　domestic　wastewater　are　used　as　denitrifiction　C-source　respectively,　the　average　maximum　NO3--N　denitrification　rate　reaches　0.75　mg/min　and　0.66　mg/min.　Finally,　sludge　reduction　rate　by　hydrolysis　and　acidification　technology　in　H-A-O　system　reaches　37%.　It　can　be　concluded　that　nitrogen　removal　efficiency　is　enhanced.