Abstract: To study the denitrification performance and mechanism of tubular bio-reactor device (TBD) filled with slow-release carbon source for domestic sewage with different nitrogen components, the actual operation effect of TBD in pilot scale under three different concentrations of dissolved oxygen (DO), ammonia nitrogen (NH₄ ⁺-N) and nitrate nitrogen (NO₃ ⁻-N) was investigated. At the same time, the change trends of environmental factors such as DO concentration, carbon-nitrogen ratio (C/N ratio), and carbon source along the TBD were monitored, and 16S rRNA diversity high-throughput sequencing of the matrix in the tube of TBD was conducted at the end of the operation period. The results showed that the removal rates of NH₄ ⁺-N, NO₃ ⁻-N and total nitrogen (TN) in sewage by TBD under three working conditions were more than 90%, proving that TBD had good denitrification performance. The slow-release carbon source contributed to the increase of C/N ratio along the TBD, and COD_Cr of TBD effluent was always lower than the Class Ⅴ standard of Environmental Quality Standards for Surface Water (GB 3838-2002), which indicated that the TBD did not produce excessive organic matter emission during enhanced nitrogen removal. Furthermore, the decrease of DO concentration along the process formed the characteristics of aerobic hypoxia distribution along the TBD and promoted the distribution of aerobic denitrification-anoxic denitrification bacteria along the TBD.