The study of security in computer networks is a key issue,which is a rapidly growing area of interest because of its importance.Main network security problems are analyzed in this paper above all,which currently are confronted with network systems and existing works in intrusion detection.And then an intrusion detection system model based on Immune Principle(IPIDS)is presented.Meanwhile,it expatiates detailed implementation of the methods how to reduce the high false positive and negative alarms of the traditional Intrusion Detection System(IDS).At last a simple simulation is performed on this model just using string match algorithm as binding mechanism.The simulation results indicate that the model can detect malicious activity effectively,and consequently the security and steadiness of the whole network system are improved also.