Submerged membranes have become one of the most competitive methods of water treatment due to the simplicity and resistance to membrane fouling compared to crossflow filtration. Since the efficiency of hollow fiber membranes depends on the dimensions of the fibers as well as filtration conditions, modeling filtration behavior of hollow fibers is important for improving design and operation of the hollow fiber system. In this study, a theoretical model based on critical flux concept was developed to simulate filtration resistance and axial pressure drop along the fiber in drinking water treatment. Depending on the characteristics of major foulant and fouling mechanisms, the behaviors of transmembrane pressure (TMP) were quite different. The major membrane fouling in surface water treatment was cake formation. Based on the model calculation, simulation of the membrane system was carried out under various conditions. The model will be useful to optimize the design and operation of hollow fiber membrane systems. Includes 15 references, tables, figures.