Improving the performance of proton exchange membrane of fuel cell (PEMFC) can save materials and then reduce costs, which is helpful to accelerate its large-scale commercial application. In this paper, an agglomerate model is proposed and developed by coupling a one-dimensional local oxygen transport model with a one-dimensional multiphase non-isothermal fuel cell model to study the influence of catalyst dimension parameters (Pt radius, Pt average dispersity, carbon radius) on local oxygen transport in the cathode catalyst layer (CCL) comprehensively. And this elaborate model shows that the smaller Pt radius, carbon radius, and the higher Pt average dispersity can reduce the transport distance of oxygen molecules from the pores to the active sites, and then decrease the local resistance. Based on the above understanding, the performance of the optimized cell with a Pt loading of 0.2 mg cm^-2 is improved by 22%, slightly higher than the original cell with a Pt loading of 0.4 mg cm^-2, which achieves a 50% reduction in Pt loading while maintaining the cell performance. This research will give a guide for improving cell performance.