This study adopted scanning electron microscope (SEM), field emission scanning electron microscope (FESEM) and the Hagen-Poiseiulle equation to determine ultratiltration membrane structure parameters, such as surface pore size, pore size distribution, porosity, pore density and so on. Based on the hydrodynamic theory from the perspective of membrane structure, the mean pore size reducing factor at and pore density reducing factor a(2) were introduced, then the model of membrane structure parameter was established, in which the pore density and mean pore size of the membrane were the major parameters. In addition, five different apparent molecular weight distribution (AMWD) water samples were used to simulate the parameters and check the model. Then, a group of parameters of a(1) and a(2) were calculated, and the influence of water characteristics on a(1) and a(2) was discussed. The results showed that the model could better reflect the UF membrane filtration process of the advanced sewage treatment. (c) 2006 Elsevier B.V. All rights reserved.