A network-based Virtual Private Network (VPN) architecture by using fundamental routing mechanism is proposed. This network is a virtual overlay network based on the relay of IP-in-IP tunneling of virtual routing modules.The packet format employs the encapsulation of IPSec ESP (Encapsulating Security Payload), an impact path code and an extended DS (Differentiated Services) code to support multi-path routing and QoS. Comparing with other models of VPN, this network system can be deployed in the current network with little investment, and it is easy to implement.The simulation result shows its performance is better than the traditional VPN system of black box mode.