In order to explore the internal flow field of the fiber filter, numerical simulation was carried out using CFD software FLUENT. This study centered on the influence of exit position of filter on the filtration efficiency, which were evaluated from velocity distribution, pressure drop, particle distribution and so on. The results showed that, the pressure drop of membranes was proportionate to the filtration velocity, while the pressure after membrane decreased with the increasing velocity. The model of side outlet had water dead zone and uneven distribution of particles which would reduce the usage rates of membrane. Placing the side outlet at the bottom of the container could effectively reduce the disadvantages. The model of bottom outlet could show the advantages of porous media more prominent than the model of side outlet.