Simultaneous nitrification and denitrification (SND) process was developed in pilot-scale tidal flow constructed wetlands (TFCW) to treat decentralized domestic wastewaters. The effects of C/N, temperature, substrate types, tidal cycles and microbial communities were investigated. Results showed that as the temperature varying from 7.1~26.8 oC, combing TFCW and activated alumina (AA) substrate could be an appropriate strategy with stable removal efficiencies of organics (82.4~90.3 %), NH3-N(72.3~84.3%) and TN (70.1~78.2%). Heterotrophic nitrifiers and aerobic denitrifiers were dominant bacteria for nitrogen removal in SND process. The activated alumina tidal flow constructed wetland (AA-TFCW) successfully cultivated and enriched heterotrophic nitrifying-aerobic denitrifying bacteria. All results demonstrate that TFCW using AA as substrate can be a useful application for treating decentralized domestic wastewaters.