Constructing backbone network reasonably is conductive to improve the ability of power grid against blackout, a novel backbone network searching method, which contains the comprehensive element importance index and network invulnerability index, was proposed. Based on the traditional electric betweenness, the economic factor was introduced to construct the index of evaluating the branch importance degree. The index of evaluating node importance degree was constructed based on the information of node neighbor and clustering coefficient. The mathematical model of backbone network including component importance degree and network invulnerability, which employed the index of invulnerability for overall network and the index of node and branch importance degree, was constructed. The guided fireworks algorithm (GFWA) that take full advantage of individual information was introduced to search the backbone network. Test result indicates that the proposed method is applicable. By introducing the network invulnerability index, the obtained backbone network can include components with high importance degrees while improving the invulnerability of networks.