The common and secure services generally exist in optical networks. For the purpose of configuring the security service to the security links for transmission, avoiding the common services occupying the security spectrum, and reducing the optical connections set-up delay of the service requests, a low delay routing spectrum assignment algorithm with service security level awareness is proposed. The algorithm divides the network physical topology into security virtual topology and common virtual topology. The service security category and link difference are fully considered. By using the security virtual topology, the security service is configured to the security link for transmission, avoiding Eve eavesdropping the effective security service data. The parallel routing strategy of the algorithm reduces the average set-up delay of the optical connections and the blocking rate of the services, and the effectiveness is verified by experimental simulation.