The three-dimensional(3D) structure distribution of granular sludge is essential to its settlement ability and stability. However, there is a lack of research on the 3D pore structure and distribution characteristics. In this study, the anerobic ammonium oxidation granular sludge was scanned through synchrotron radiation X-ray phase microscopic computed tomography，with its structure being reconstructed by Avizo. The diameter, spatial distribution, and fractal dimension of the pore structure were obtained to establish the pore network model of granular sludge. Subsequently the calculation of absolute permeability was made. It is hoped that this research will make a contribution to the theoretical basis for the stable and efficient application of granular sludge system in sewage treatment.