This paper proposes a kind of network connectivity analysis algorithm-node combination method based on the graph theory. It uses the two terms of adjacency island and connective island to illustrate the principle of combining the adjacency islands into a connective island in a graph, and to introduce the method of marking the label number of a adjacency island and a connective island. After the finishing of the algorithm, the network connectivity is recognized according to the connective island's of each node in the graph. The computing complexity and time complexity are proportional to the total number of nodes in a graph. The analysis of its algorithm and the results of examples show that the node combination algorithm is an effective tool to complete different structure's network topological division.