Based on the introduction of mobile agent , the advantage of intrusion detection system using mobile agent technology is elucidated , and a mobile agent based intrusion detection system( MAB - IDS) is presented in this paper. The paper discusses the architecture of system in detail , as well as the means of intrusion detection and its working principle. By comparing with other systems in this area of research , It is concluded that the application of mobile agent technology makes MAB - IDS have a better capability of intrusion detection.