The invention discloses a network topology information server for realizing relay selection. The network topology information server stores network topology information and operator strategy information and comprises a relay service unit, wherein the relay service unit comprises a relay selection module and/or a relay sequencing module. The invention also discloses a system and a method for realizing the relay selection. The function of the existing network topology information server is expanded, so the network topology information server can support the relay node optimization function, in addition, a corresponding interface can be provided, the utilization rate of the network topology information and the operator strategy information is greatly improved, the data maintenance load and the operation load of a relay management entity are greatly reduced, in addition, the timely updated network topology information is adopted, the work efficiency of the relay management entity is effectively improved, and in addition, the relay selection accuracy can be ensured.