The rheological behaviour of the low sludge concentration liquor in MBR was investigated and made a conclusion that this liquor approximated to the Newtonian fluid while the concentration of the sludge was less than 8000 mg x L(-1). Furthermore, when the laminar flow boundary layer thickness on the surface of flat membrane came up to the thickness of precoated dynamic membrane (PDM), the steady aeration intensity was calculated by using the boundary layer theory in the Newtonian hydrodynamics. In order to ensure the stability of the pre-coated dynamic membrane bioreactor (PDMBR), oxygen supply aeration intensity was chosen to supply the best dissolved oxygen (3-5 mg x L(-1) in the initial stages and gradually increased to the steady aeration intensity. The results indicated that this mode could enhance the stability of PDM. In the experiment period (31 d), effluent COD was less than 12.48 mg x L(-1) and its average removal rate was 97.49%, NH4+ -N was less than 5.27 mg x L(-1) and its average removal rate was 76.13%, while the operational pressure just increased to 27 kPa. During the last period of the experiment, the stability of the PDMBR was studied when the aeration intensity was more than the steady aeration intensity and it was found that the precoated layer had been brushed off from the surface of common filter cloth, so this phenomenon proved that using the boundary layer theory could determine steady aeration intensity of PDMBR.