The present disclosure relates to the field of communications technologies and discloses a method, a device, and a communication system for establishing a connection with a network management system. The method includes: obtaining, by a relay node, a first IP address of the relay node; obtaining, by the relay node, an IP address of a security gateway by using the first IP address of the relay node; establishing, by the relay node, an IP security tunnel with the security gateway according to the IP address of the security gateway; obtaining, by the relay node, a second IP address of the relay node and an IP address of the network management system through the IP security tunnel; and establishing, by the relay node, a connection with the network management system by using the second IP address of the relay node and the IP address of the network management system.