In wireless sensor network, virtual backbone is a cost effective broadcasting method. Connected dominating set formation is proposed to construct a virtual backbone. However, it is NP-Hard to find a minimum connected dominating set in an arbitrary graph. In this paper, based on cross-entropy method, we present a novel backbone formulation algorithm (BFA-CE) in wireless sensor network. In BFA-CE, a maximal independent set is got at first and nodes in the independent set are required to get their action sets. Based on those action sets, a backbone is generated with the cross-entropy method. Simulation results show that our algorithm can effectively reduce the size of backbone network within a reasonable message overhead, and it has lower average node degree. This approach can be potentially used in designing efficient broadcasting strategy or working as a backup routing of wireless sensor network.