The objective of this study is to develop a 3D DMFC model for modeling gas evolution and flow patterns to design optimal flow field for gas management. The gas management on the anode side is important issues in DMFC design and they greatly influence the performance of the fuel cell. The flow field is tightly related to gas management and distribution. Since experiment for the optimal design of various flow fields is difficult and expensive due to high bipolar pate cost, computational fluid dynamics (CFD) is implemented to solve the problem. A two-fluid model was developed for CFD based flow field design. The CFD analysis is used to visualize and to analyze the flow pattern and to reduce the number of experiments. Case studies of typical flow field designs such as serpentine, zigzag and parallel type illustrate application of the model. This study presents simulation results of velocity and pressure. The suggested model is verified to be useful for the optimal flow field design.