The release of drug from a polymeric matrix is complicated. It often involves drug diffusion, interface movement and various interactions. It also shows a dependence on the length of polymer rod. With Lc as the 'critical length', three different phases can be distinguished from the kinetic process. Prior to reaching Lc, the interface movement plays a key role on determining the release. Otherwise, the drug diffusion can dominate the release process. Near Lc, however, both factors are involved. The rate of interface movement is closely associated with the time and position in the polymer rod. Taking these characters into account, a common model is presented in this article to be tentatively used to interpret the release process. These results provide preliminarily an insight into the understanding of controlled release process.