Abstract Reducing Platinum amount in proton exchange membrane fuel cell (PEMFC) is one of the main tasks to achieve low cost PEMFC. Recently, significant performance loss has been found under low Pt loading due to local mass transport limitations. In this study, pore-scale simulations are conducted to study oxygen transport within four-constituent microscopic structures of catalyst layer including a carbon particle, ionomer, Pt particles, and primary pores inside the carbon particle. Multiphase physicochemical processes are considered, including oxygen dissolution at the pore/ionomer interface, oxygen diffusion within the ionomer film and inside the primary pores, and reactions at the Pt interface. Local transport resistance is calculated based on the pore-scale concentration field predicted. The simulation results are compared with existing experimental results and 1D models. Simulation results show that dissolution resistance at the secondary pore/ionomer interface is about 10–50 times higher than that inside the ionomoer. Local transport resistance increases as Pt loading decreases, especially under Pt loading of 0.1 mg cm−2. Besides, local transport resistance can be reduced by depositing more Pt outside the carbon particle, alleviating agglomeration and/or decreasing the ionomer thickness. The simulation results indicate that local transport characteristics should be considered when developing 1D agglomeration model of catalyst layer.