Abstract: Fuel cells have received extensive attention due to their high efficiency, low cost, and environmental friendliness. During the operation of the fuel cell, the microstructure change of the air cathode and the distribution of liquid water will affect the mass transfer of the gas, which in turn affects the discharge performance of the cell. The visualization technology of the electrode can effectively obtain the microstructure information of the air cathode, which provides an important reference for the research of the air cathode. At present, X-ray computed tomography (X-ray CT) and focused ion beam combined with scanning electron microscopy (FIB-SEM) are the most widely used techniques to characterize the microstructure of fuel cell air cathodes. In this paper, the research on the microstructure, liquid water distribution, lifetime and mass transfer of fuel cell air cathodes are reviewed by two 3D reconstruction techniques, X-ray CT and FIB-SEM.