Computer virus is a malicious code which can causes great damage. A SEIR model is proposed which considered that the newly entered computer in the network has been infected by other ways. It is concerned with the constant immigration, which includes susceptible, exposed and infectious, the threshold and equilibrium of this model are investigated. The locally and globally asymptotical stable results of virus-free equilibrium and viral equilibrium were being proved. Finally, some numerical examples are given to demonstrate the analytical results.