The backbone network is the main part of the Internet traffic transfer system, and the router-level topology of backbone network is of great significance for the research on network survivability. Due to various reasons, it is difficult to get real Internet backbone router level topology. By analyzing the forming driving factors of backbone network, the geographical constraints, the exchanging strength of nodes, infrastructure cost and robustness, etc. were combined; the router-level topology generation method for Internet backbone networks under multiple constraints was proposed. The method can generate router level topology for network which cannot be inferred from publicly accessible measurement data, and can generate topology set that consists of realistic alternatives for a backbone network. Finally, the effectiveness of the method is verified by two real Internet backbone networks. 