Anammox process is a new biotechnology for nitrogen removal from wastewater. It has become one of the research hotspots and has been put into wide used in wastewater treatment engineering. Anammox reactor based on granular sludge bed is a high-rate bioreactor. The biophase in the form of granular sludge is the key factor that determines the reactor performance. It can be divided into three structures from macroscale to microscale:sludge bed

granular sludge and bacterial cell. The morphological and functional characteristics of three structures and their relation with reactor performance are reviewed so as to give guidance for online optimization and process control.