Particle size analyzer, scanning electron microscope were used to investigate the dynamic membrane composition and filt ration performance under optimal operation parameters. Energy disper sion spect roscopy was used to determine the elemental composition of the dynamic membrane. The results indicated that the mass concent ration of cake layer was 39.27g?m-2, with contents of colloid, volatile suspended solids and inorganic matter 5.75g?m-2, 26.5g?m-2 and 7.02g?m-2 respectively. Self-generated dynamic membrane mainly consisted of porous structure with high porosity. Filamentous bacteria which acted as matrix of dynamic membrane structure could be obviously observed. Most of teparticle size range from 70μm to 130μm?O, K, Na, Ca, P, S, Cl, Mg, Si were the main elementsin t he dynamic membrane.