To investigate the effect of redistribution of phosphoric acid in the catalytic layer of high-temperature proton-exchange membrane fuel cells on the electrode performance, focused ion beam-scanning electron microscopy was employed to image the in-house gas diffusion electrode, and a three-dimensional model of the catalytic layer was reconstructed. By using multiple relaxation-time-lattice Boltzmann model to simulate the migration and redistribution of phosphoric acid in the catalytic layer, two different phosphoric acid distribution forms (decreasing type and quasi-uniform type) were obtained. Pore-scale modelling was used to examine the electrode transmission properties under different conditions. The results show that when the phosphoric acid content is low, the quasi-uniform phosphoric acid distribution has slightly larger electrochemical active surface area and slightly lower effective diffusion coefficients of oxygen and water vapor. When the content of phosphoric acid is high, the electrochemical active surface areas of the two distribution types are similar, but the quasi-uniform distribution has higher effective diffusion coefficients of oxygen and water vapor.