The principle of the MBBR process is to increase the biomass and species in the reactor by adding a certain number of suspension carriers to the reactor, so as to improve the treatment efficiency of the reactor. Because the density of the filler is close to that of water, it is completely mixed with water during aeration, and the environment for microbial growth is gas, liquid and solid. The collision and shear effect of the carrier in the water makes the air bubbles finer and increases the utilization rate of oxygen. In addition, each carrier has different biological species inside and outside, some anaerobic bacteria or facultative bacteria grow inside, and the outside is good trophic bacteria, so that each carrier is a miniature reactor, so that nitrification reaction and denitrification reaction exist at the same time, so as to improve the treatment effect. The MBBR process has the advantages of both traditional fluidized bed and biological contact oxidation method, and is a new and efficient sewage treatment method, which relies on the aeration and water flow in the aeration tank to make the carrier in a fluidized state, and then forms suspended activated sludge and attached biofilm, which makes the moving bed biofilm use the entire reactor space, give full play to the advantages of both the attached phase and the suspended phase organism, and make it develop its strengths and avoid weaknesses, and complement each other. Unlike conventional fillers, suspended fillers are called "mobile biofilms" because they are in frequent and repeated contact with sewage.