Distributed denial of service(DDoS) attack is a major threat to cyber space.According to the similarity of DDoS and MAS in position distribution and behavior characters,simulation models of DDoS attack and defense based on MAS were designed and implemented.At first,different attack agents based on the roles they play in DDoS attack process were abstracted and established,including master agent,midway agent and controlled agent.And then,data collecting agent,attack detecting agent and victim response agent were designed.These agents consisted of DDoS defense simulation system.At last,these agents were carried out and DDoS attack and defense were simulated.With the joint execution of DDoS attack and defense agents,new styles of DDoS attack could be not only studied,but the technologies of DDoS defense could be also explored and analyzed.