Domestic　wastewater　was　treated　with　activated　sludge　system　and　activated　sludge-biofilm　system　at　low　temperature　(10　degrees　C),　respectively.　In　both　systems,　step-feeding　strategy　were　adopted　while　the　aerobic　and　anoxic　zones　were　designed.　The　performances　of　two　different　systems　were　compared.　The　microbial　community　in　the　activated　sludge-biofilm　system　was　studied　deeply.　As　a　result,　the　activated　sludge-biofilm　system　achieved　higher　performance　than　the　activated　sludge　system.　In　the　activated　sludge-biofilm　system,　the　chemical　oxygen　demand　(COD),　NH4+-N　and　total　nitrogen　(TN)　removal　efficiencies　reached　88%,　97%　and　65%,　respectively.　However,　in　the　activated　sludge　system,　the　COD,　NH4+-N　and　TN　removal　efficiencies　were　86%,　40%　and　55%,　respectively.　Simultaneous　nitrification　and　denitrification　(SND)　occurred　in　aerobic　zones　in　activated　sludge-biofilm　hybrid　system.　The　effluent　TN　concentration　was　8.5　mg/L　in　average,　which　was　mainly　contributed　by　NO3--N.　The　main　microbial　communities　consisted　of　Proteobacteria,　Bacteroidetes,　Nitrospirae,　Firmicutes,　and　Planctomycetes　were　at　the　phylum　level,　indicating　the　occurrence　of　nitrification,　denitrification,　and　anammox.