Abstract: This study was conducted to explore nitrogen transformation and associated microbial characteristics in a tidal flow constructed wetland (TFCW) with the complete autotrophic nitrogen removal over nitrite (CANON) process under influent COD/TN (C/N) constraints. The influent C/N increased from 0.0 to 10.0 via the addition of glucose in the influent as a source of organics. The results showed that influent C/N significantly affected nitrogen transformation rates in the TFCW throughout the experiment. As the influent C/N increased from 0.0 to 6.0, the absolute abundance of functional genes involved in denitrification could be enriched as a consequence of the addition of organics in influent, and then the simultaneous nitrification, anammox, and denitrification (SNAD) processes occurred in the TFCW, resulting in the enhancement of nitrogen removal in the system. However, as the influent C/N was more than 6.0, the activity of aerobic ammonia-oxidizing bacteria was inhibited and its quantity reduced, leading to the deterioration in nitrogen removal of the system. When the influent C/N was 6.0, the SNAD process was enhanced most effectively in the system owing to the development of multiple and complete nitrogen removal pathways in the TFCW. The TFCW respectively had the best TN removal efficiency and removal loading rate [(93.3±2.3)% and (149.30±8.00) mg·L^-1·d^-1], indicating that the results had been than the maximal TN removal efficiency in a CANON process under ideal conditions.