With the rapid development of modern network technology, communication network has been further researched, and the reliability of network is one of the major criteria to evaluate the performance of network. With the previous theories researches and practice about network, this paper evaluates the importance of node and link state according to the node deletion and link contraction method respectively, then make appropriate adjustments, we propose a new method—TNL algorithm based on the inherent network topology, combined with transmission characteristics. This method evaluates the reliability of network with different network topologies effectively, experimental results demonstrate the efficiency of the proposed algorithm which is better than BDD algorithm.