Abstract: In this study, alkali-soluble polysaccharide was extracted from Poria residue, and the structure of alkali-soluble polysaccharide was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), and differential scanning calorimetry (DSC). The physical morphology of alkali-soluble polysaccharide and ethyl cellulose (EC) was investigated by scanning electron microscopy (SEM), and the focus on angle of repose, bulk density, tapped density, Carr index, interparticle porosity, cohesion index, Hausner ratio, etc. The physical fingerprints were drawn, and the powder properties were evaluated by multivariate analysis. Diclofenac sodium extended-release tablets were prepared by direct compression method using alkali-soluble polysaccharide and EC as insoluble backbone materials to evaluate the basic properties of the extended-release tablets, investigate the in vitro drug release behavior and study the release mechanism. The results showed that alkali-soluble polysaccharide is a semi-crystalline polymer with smooth lamellar structure, and its stacking and compressibility are stronger than EC. The in vitro release experiments showed that the slow release performance of alkali-soluble polysaccharide is stronger than EC, and the release behavior of the prepared slow release tablets is in accordance with the Higuchi model. The pore structure is formed inside the tablets during the release process, and the release mode is pore diffusion release. The results of this study are of great significance for the development of new slow-release materials and the rational use of resources.