In this paper, we select the key nodes from the software network by selecting the propagation domain as the standard and propose a method of fast locating key nodes based on the distribution law of node's propagation domain. Firstly, a reasonable sample node is used to quickly obtain the critical propagation domain threshold as a screening criterion. And filtering the key nodes with this threshold can significantly reduce the total traversal workload. In order to further reduce workload, this paper proposes a filtering method of critical nodes that threshold is based on the number of packets that the nodes can affect. After a number of experiments, the result shows that the proposed method can effectively reduce the traversal workload of locating key nodes.