The networked air and missile defense system has the ability to flexibly control combat resources， effectively realize dynamic cross-domain command and control， and efficiently complete combat tasks. However， networked and integrated operations increase the risk of weapon systems suffering from cyber attacks while improving combat effectiveness， which will seriously threaten network security and combat effectiveness of combat equipment. Taking the U.S. tactical-level air and missile defense system as an example， according to its networked combat characteristics， this paper analyzes the security vulnerabilities of the air and missile defense network， and constructs an assessment model to analyze the probabilities of destroying network nodes. Three indicators are designed and used to evaluate the network performance loss of the node suffered network attack. The OPNET platformand the NetworkX are used to carry out network simulation experiments. Based on the evaluation results， the network defense strategies are proposed to provide reference for the improvement of the security defense capability.