Recently, low pressure membrane filtration using hollow fiber modules have been widely applied to water treatment and wastewater reuse for its simplicity and compactness. Nevertheless, understanding hydrodynamics in hollow fiber membrane modules is challenging because the efficiency of hollow fiber membrane modules depends on the dimensions of the fibers as well as filtration conditions. Thus, modeling filtration behavior of hollow fibers is important for optimization of performance of hollow fiber system. In this work, a mathematical model was developed to provide insight into the design of fullscale hollow fiber membrane modules. The model was verified with experimental data from a laboratory-scale membrane filtration equipment. Based on the model calculation, the effect of flux variations along the filter on filtration characteristics was investigated. The model was also applied to set up a new strategy to develop new hollow fiber membranes with unique dimension and properties. Both pressure and submerged types of membrane modules were considered. The model calculations indicated that the geometry of fiber and module is crucial. A long fiber with a small inner diameter results in a large difference in local flux along the fiber under non-fouling conditions. A rapid increase in trans-membrane pressure was expected under fouling conditions. In most cases, a fiber with large inner diameter and small thickness (in other words, relatively small outer diameter) is found to be efficient as long as its mechanical strength is large enough. Considering all these factors, the optimum range of module geometry was estimated to minimize loss by pressure drop and energy consumption. In addition, the optimization conditions from our modeling results were compared with previous works.