Based on betweenness centrality of complex network theory

concept of betweenness centrality of wireless sensor networks（ WSNs） node is proposed

and this method is applied to assess importance of each node of WSNs. Based on WSNs structure entropy

combined with its character of WSNs

betweenness entropy measurement model is given

to measure invulnerability of networks. Simulation indicates that this model can objectively and accurately assess invulnerability of WSNs.