Abstract: Active microorganisms on biofilms play a decisive role in the transformation-transportation process of pollutants in aquatic environment. An ATP bioluminescence method of environmental biology was used in this study to investigate the influence of active microbial biomass on the kinetics of phosphorus adsorption onto biofilms and explore the mechanism of how these microorganisms are acting in the adsorption. The results show that for the biofilms cultured in natural water, their active microbial biomass increases with culture time and reaches a stable stage after three days of culturing while their phosphorus adsorption capacity varies considerably across different growing stages and reaches the maximum at the seventh day. Obvious correlation has been found between phosphorus adsorption and microbial biomass, and the adsorption process can be divided into four typical stages. In addition, flow velocity, light, nutritional status, and pH are also major factors that affect the kinetics of phosphorus adsorption by microorganisms on biofilms. The quantity of active microbial shows high stability in solutions of high pH level, and an alkaline environment promotes the phosphorus adsorption.