Abstract: The credibility of routers and forwarding paths in the Internet has been a popular topic. Not only network equipment of different vendors, but also the same one in different management environments has different credibility. The network flows with diverse credibility requirements are supposed to be transmitted along paths with the corresponding credibility levels (CR). In this paper, the credible transmission mechanism with multiple levels (CETML) is proposed, and the fundamental credible management strategies are suggested. Both routers and IP prefixes are associated with a CR, and the CR of a network flow is obtained according to its source and destination IP addresses. CETML constructs different virtual topologies for every transmission network with different CR, and insures that IP packets is forwarded by the routers whose CR is not less than the CR of these packets. Because the forwarding entries include multiple next hops, a small quantity of additional memory overhead is introduced in CETML. Analyzing the relevancy of the multi-level virtual topologies, we design a new routing calculating method based on Floyd algorithm in SDN environment. All the routing tables of virtual topologies can be achieved during the process of successive iterating calculation. Compared with current typical routing algorithms, the calculation time of CETML is significantly reduced.