Abstract: To avoid the weakness of DoS attack,Reduction of Quality Attacks(RoQ) utilizes the security vulnerabilities in self-adaptive mechanism of network and terminal system by sending high strength pulse intermittently,thus reducing the service quality of victims．RoQ attacks are more elusive and efficient,which brings challenges to its detection and evaluation．Right now the defense technologies to RoQ attacks mainly include mending protocol,detection of attack flows’ features,self-adaptive detection and repairmen,and so on．This paper builded a Stochastic Petri Net(SPN) and used it in SPNP software to simulate the service quality changes in the process of attack and defense game．By evaluating the effects of different defense ways,this paper offered some consultancy for decision-makings in cyber defense activities．

Key words: SPN,RoQ,Attack and defense game,Effect evaluationa