In order to improve reliability of wireless sensor network,a new reliability analysis method of wireless sensor networks is proposed based on binary decision diagrams and fault tree in this paper. Firstly,fault tree model is built based on hierarchical clustering topology of wireless sensor networks, and then the network fault tree of topology structure is converted into binary decision diagrams structures. Finally,the simulation experiment is carried out to test the performance under different performance criterion such as node redundancy and different hops between nodes. The results show that the proposed method can provide useful message for the performance optimization of wireless sensor network and improve the reliability of wireless sensor network .