An important prerequisite for normal operation of wireless sensor networks（ WSNs） is whether energy of network nodes is sufficient or not

therefore

research on energy efficiency of WSNs has been a hot and difficult problem in this field. Study on end of energy efficiency of node

called node vulnerability is carried out

and it is analyzed that the topological characteristics and node vulnerability of WSNs has important meaning to optimize node energy and improve life cycle of networks. Topological network model is built by means of Space D method

average path length

node degree

clustering coefficient

other specifications and distribution rules are analyzed by Matlab 7. 0

energy vulnerability chart of each node is labelled

the biggest key node which affects network life cycle is found. Simulation experimental result shows that nodes covered by area where change of water quality is large large amount of data transmission

which result in energy consumption is too fast

and effect of these node on network efficiency is the maximum

at the same degree.