By incorporating time delay into the immune response, the authors proposed the following viral model
where are the numbers of susceptible host cells, virus population and cytotoxic T lymphocytes at time respectively, and all the parameters are positive. Then the stability of the equilibria and the permanence of the system are proved. Moreover, some numerical simulations are given to illustrate the complex dynamic behavior of the system, including the periodic solution, chaos and stability switches. The results in this paper imply that the basic reproductive ration of the virus is an important index in understanding the long time behavior of the immune state of patients.