A new network intrusion detection model based on immune multi-agent theory is established and the concept of multi-agents is advanced to realize the logical structure and running mechanism of immune multi-agent as well as multi-level and distributed detection mechanism against network intrusion, using the adaptability, diversity and memory properties of artificial immune algorithm and combing the robustness and distributed character of multi-agents system structure. The experiment results conclude that this system is working pretty well in network security detection.