Understanding the three-dimensional(3D) structure distribution of granular sludge is crucial for its settlement ability and stability, yet research on the 3D pore structure and distribution characteristics remains scarce. In this study, anerobic ammonium oxidation granular sludge is scanned using synchrotron radiation X-ray phase microscopic computed tomography,and its structure is reconstructed using Avizo. The diameter, spatial distribution, and fractal dimension of the pore structure are analyzed to establish a pore network model for granular sludge. Subsequently, absolute permeability calculations are performed. This research contributes to the theoretical foundation for the stable and efficient application of granular sludge systems in sewage treatment.