Granular layer filtration is widely used in the treatment system of oilfield produced water, and water distribution of granular layer filter which directly affects the purification effects of produced water plays the same significant role as the selection and arrangement of granular layer. The model of filter was built and unstructured grids were generated by Gambit. The flow rate field in the model was calculated by Fluent combined with DPM model. Based on the DPM model in Fluent software, a numerical simulation of pressure field distribution, filtration pressure drop along the axis, pathlines of particles, and particles distribution and aggregation behaviors were simulated and calculated. Then, water distribution characteristic in pressure filter of produced water was described, and optimization of water distribution process was realized. The results showed that the good performance of water distribution was obtained and the pressure drop in the filter with sieve tubes was reduced by 30.56% compared with the filter with slots. Furthermore, the filter with nine sieve tubes was optimized by its excellent water distribution characteristic. Such a numerical simulation method can provide effective support for optimization of filtration process and purification of produced water.