Abstract: Ammonia-oxidizing microorganisms (AOMs) regulate the first step of nitrification in the geochemical cycle of nitrogen, which can oxidize NH₃ in the habitat to nitrite NO₂^-.With the in-depth study of the function and role of microorganisms in geochemical cycling, the study of ammonia-oxidizing microorganisms in the major estuaries and oceans has also attracted much attention.AOMs has different niche differentiation in different environments.The abundance of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) is significantly different in estuarine and marine environments, and the community structures of AOB and AOA are also significantly different.In estuaries and oceans, environmental factors such as salinity, temperature, nitrogen content, carbon content and dissolved oxygen are significantly different.Analyzing the effects of different environmental factors on AOMs and understanding the spatiotemporal dynamics, community structure change and niche differentiation characteristics of AOMs are the theoretical basis for studying microbial nitrogen geochemical cycle.