Tree-like branching structures occur in both natural and artificial transport systems, which have fascinated multidisciplinary researchers to study and apply the transport mechanisms of tree-like branching structures for decades. In this paper, the flow field of a proton exchange membrane fuel cell (PEMFC) with a Y-shaped tree-like fractal structure was studied utilizing Murray’s law in fractal theory. The polarization curve, gas concentration distribution, water concentration distribution, pressure drop distribution, and current density distribution of the PEMFC are numerically simulated in this research, and the transmission law is analyzed with different channel branching angles [Formula: see text]. The results demonstrate that the optimal branching angle of the designed tree-like fractal flow field is [Formula: see text]. When compared to a parallel flow field under identical conditions, the maximum output power density of the fractal flow field with a branching angle of [Formula: see text] is 26.7% higher. The optimal angle of [Formula: see text] for symmetric branching flow derived from Murray’s law was shown to be applicable to the flow field design of the fuel cell, improving the transport characteristics of the reaction gases and the overall performance of the PEMFC. This research may provide further references for the design of flow fields in fuel cells.