The discovery of complete ammonia oxidation (comammox) bacteria was one of the major hotspots in microbial nitrogen cycle fields, and thus caused widespread concern about their global distribution, phylogenetic characteristics, physiological and biochemical properties. This review first summarizes the distribution pattern of comammox bacteria in soil, surface water, wastewater treatment systems, etc, then expounds the mechanism of interaction and niche separation between comammox bacteria and traditional nitrifying microorganisms from the aspects of substrate affinity and metabolic diversity. Based on the above, coupling of comammox bacteria with other denitrifying microorganisms, e.g, denitrifying bacteria, anaerobic ammonia oxidizing bacteria, and anaerobic methane oxidizing bacteria, is proposed to achieve advanced wastewater nitrogen removal under low ammonia and dissolved oxygen conditions, thereby saving energy consumption and reducing greenhouse gas emission. Future research should focus on identifying the physiological and biochemical characteristics of comammox bacteria, evaluating the ecological function and contribution to the biogeochemical nitrogen cycle, and then sequentially tapping their application potential in biological wastewater treatment process and other fields.