Abstract: How to find the key nodes in the networks is critical to distribute the limited networks security resource for the key part in the networks, so that the key parts of the networks can operate effectively under the attack of the network threat. In this study, we divide the network into nodes and edges according to the graph theory and study the node importance of the networks by means of the complex network. First, the topological model of the network is modeled by means of complex networks theory under the base of analyzing the connection feature and the function of the network firstly and then some characteristics of the networks are presented, such as the information distribution amount, distribution efficiency and the information control capability; finally, an evaluating algorithm of node importance for the networks is proposed based on the relation, function of the nodes and the properties of the network. The simulation result shows that the method of node importance proposed in this study is effective and therefore a reference can provided for making network defense decision.