A dynamic membrane bioreactor (DMBR) was developed by substituting dynamic membrane (DM) for the separation membrane in the submerge membrane bioreactor. The formation mechanism and structure of dynamic membrane were investigated. Firstly. based on the flux behaviors of dynamic membrane under constant filtration pressure, the formation mechanism of dynamic membrane was assumed in a creative way by dividing the formation process of dynamic membrane into four stages, which was then proved by four classic filtration laws. Furthermore, by the proposed formation mechanism, dynamic membrane from inner to outer was divided into three layers, namely substrate layer, separation layer and fouling layer. Moreover, by combining the theory of hydrokinetic boundary layer with the formation mechanism of dynamic membrane, the methods for calculating the optimum cross-flow velocity on membrane surface and aeration amount for controlling membrane fouling were provided. (C) 2008 Elsevier B.V. All rights reserved.