Abstract: In order to study the release mechanism and control release performance of porous microspheres, the Parsol 1789 was chosen as the model hydrophobic ingredient, by taking consideration of diffusion equation and dissolution theory. A new dissolution diffusion model was developed for description the cumulative release amount in different time. The model was used to fit the release profiles of three actives with different solubility, and the diffusion coefficient and dissolution rate constant were obtained. The results show that different preparation methods and compositions have important influence on diffusion coefficient, whereas the dissolution rate constant is decided mainly by the actives properties.