Enterprise network constructed through VPN technology has many problems including scalability, device address confliction, difficulty in realizing mutual access control. As to the problems, the paper proposes the idea of constructing an integrated VPN which integrate the effective solutions in order to solve different problems on the basis of making analysis on the reasons for these problems. The idea also solves the problem of tunnel scalability by MPLS and gets the solution to address confliction and access control by BGP. In addition, In order to evaluate the performance of this design method, it applies the idea to construct actual VPN in enterprise network. Practice result has proved this method is superior to VPN technology in scalability, device address conflict, access control, and VPN technology.