Abstract: Network routing-based attacks have become more common and the attack consequence can be more serious than other traditional network attacks. Most schemes on improving routing data security are applied to current routing protocols, e.g. digital signature, message authentication and intrusion detection, etc. But very few design guidelines on how to select a secure path to forward confidential user packets. By analyzing the security mechanisms and security threats over network entities, trust degrees of communication links and routers are measured and trust relations are built among network routers. Based on the trust model, a novel SM (Security Metric) is further defined and quantified as the routing criterion used in the proposed security routing algorithm SMRA (Security Metric based Routing Algorithm). Simulation results show that SMRA gets better performance than OSPF in terms of packets delivery ratio and routing security in unsafe networks.