Abstract:Hydroxylamine, as an important intermediate product in the nitrogen cycle, connects ammonia oxidation and nitrite oxidation, influencing the velocities and directions of processes like ammonia oxidation, nitrite oxidation, and denitrification. Because of the close associations with the generation of N2O through enzymatic reactions and self-decomposition or reactions with other substances, hydroxylamine has become a focus and hotspot of research. This paper summarized the generation and transformation of hydroxylamine in autotrophic and heterotrophic ammonia oxidation, the key role of hydroxylamine in the nitrogen cycle, and the promoting effect of hydroxylamine on N2O emissions. It analyzed the processes of autotrophic and heterotrophic ammonia oxidation and their enzymatic differences, aiming to provide a theoretical reference for in-depth research on the role of hydroxylamine in the microbial nitrogen cycle and for the research and development of measures to reduce N2O emissions and protect the atmospheric environment.