In this paper,each deactivation of catalyst for start,middle,and end of run in the hydrodesulfurization (HDS) process is theoretically interpreted as the behavior due to the reduction of active sites and effective diffusivity that is caused by coking and deposition of metal (Ni, V). In the previous report, catalyst deactivation in HDS was viewed as a model of simple simultaneous equations assuming that deactivation was the sum of first -order reduction rate of different active sites. In this study, furthermore,based on a long-term test using Arabian heavy atmospheric residue, a deactivation model due to diffusivity within the catalyst pores is made and an overall deactivation equation interpreting the ail behaviors of deactivation through a HDS run is developed by adding the diffusion model to the previous active site model. In this report,the concept of the new kinetic model and method to determine the deactivation parameters that compose the overall deactivation equation are described, and also various catalyst deactivations in HDS of light and heavy oils are analyzed by the new equation,The analytical results agree with all deactivation behaviors. Furthermore,the deactivation parameter obtained by analysis are discussed with the physical properties of the catalysts, and the applicability of the overall deactivation equation is also referred.