Abstract: A security evaluation model based on routing attack effect was introduced to improve the ability of WSN's safety evaluation. Network security entropy was argued to describe the security change after routing attack, we also chose appropriate index and predigested it, to analyze the calculating method of network security entropy. Applying Monte Carlo Method, we got the degree of security, and the security index should be unitary, then we evaluated the security of system and forecasted safe situation by calculating attack effect. Then the ability of WSN's security evaluation could be improved and the model provided basis for better method to resist attacks from enemy. Imitation and analysis of case studies shows that the model is oppropriate for security evaluation.

Key words: WSN, Routing attack effect, Network security entropy, Monte Carlo method