Constructed wetland (CW) is popular in wastewater treatment for its prominent advantage of low construction and operation cost. However, the nitrogen removal in conventional CW is usually limited by the low dissolved oxygen (DO) and insufficient electron donor. This paper investigated the nitrogen removal performance and mechanisms in the poly (butylenes succinate)-based CW (PBS-CW) while treating ammonia wastewater under different DO levels. The average DO contents in limited-aeration and full-aeration phases were 1.68 mgL(-1) and 5.71 mgL(-1), respectively. Results indicated that, with the ammonia nitrogen loading rate of 25 g N m(-3) day(-1), total nitrogen removal ratios in the PBS-CW under the limited-aeration and full-aeration phases were 72% and 99%, respectively. Combined analyses revealed that simultaneous nitrification and denitrification (SND) via nitrite/nitrate were the main microbial nitrogen removal pathways in the aeration phase of the PBS-CW (>89%). The microbial carrier of biodegradable material was believed to play a significant role in prompting SND performance while dealing with low C/N wastewater. Due to the coexistence of micro-anaerobic zone and carbon supply inside the coated biofilm, the high DO level in the PBS-CW increased the abundance of the nitrifying bacteria (amoA and nxrA), denitrifying bacteria (narG, nirK, nirS, and nosZ), and even anammox bacteria (anammox 16s rRNA). These features are beneficial to many microbial processes which require the simultaneous aerobic, anoxic, and anaerobic environment.