Abstract: This paper presents a new Mobile Agent Distributed IDS (MADIDS) system basing on the mobile agents. This system is specifically designed for WAN, In MADIDS, the agents that are set at each node process the data transfer by distributed computation architecture. It has the ability of intrusion detection within the entire network and has good portability. The consumption of the network and servers' resources is not high, which means the possibility of network bottleneck is decreased. In this paper, we construct the infrastructure and theoretical model of MADIDS, and the deficiencies of MADIDS and future research work are also indicated.