Abstract: An experimental equipment was designed to measure the diffusion rate of gases through the ring-shaped, cylindrical or tabletted catalyst, using this equipment and the constant total pressure, steady-state technique, the tortuosity of Z-type natural gas steam reforming calalyst has been determined, with gas systems of CH4-He, N2-He and N2-CH4 at ordinary temperature and pressure. The results obtained for different gas systems quite close each other, the tortuosity of the catalyst is about 2.3.