Abstract: On the basis of analyzing the evolution and drawbacks of current intrusion detection systems（IDS）, a novel intrusion event correlation system（ECS） based on interactive knowledge discovery is proposed. ECS is composed of off-line part and on-line part. As the former, FP Tree and WINEPI algorithms are first introduced to implement interactive knowledge discovery for intrusion events correlation. And the discovered frequent patterns and sequence patterns are converted into associative rules for the inference of intrusion events. As the online part of the ECS, embedded CLIPS inference engine is employed to do event correlation, based on priori knowledge and the associative rules discovered above. Application of the ECS in the integrated network security monitor and defense system named Net-Keeper shows that the proposed system is an open and efficient intrusion event correlation engine.