A constructed wetland (CW) is an effective technology for the treatment of nitrogen (N) pollution in water bodies, with microorganisms being important engines driving N-removal. Over the past two decades, with the development of culture-independent molecular techniques, break-through progress has occurred in microbial ecology for N-removal in CWs. Nitrification-denitrification and anammox processes have been recognized as the two main microbial pathways for N-removal in CWs. In the present study, we reviewed the available literature regarding research progress in N-removal communities including archaeal and bacterial ammonia oxidizers, anammox bacteria, and denitrifying bacteria in CWs. Case studies on bacterial abundance, activities, diversity, distribution, influence factors, and contribution to N-removal are summarized, and future perspectives for this research field are presented. Future microbial ecology studies of N-removal in CWs should focus on the role of microorganisms in purification of sewage and emission reduction in greenhouse gases, and improve research on their N-metabolic processes, mechanisms, and interactions.