Application of data fusion technique in intrusion detection is the trend of nextgeneration Intrusion Detection System (IDS). In network security, adopting security early warning technique is feasible to effectively defend against attacks and attackers. To do this, correlative information provided by IDS must be gathered and the current intrusion characteristics and situation must be analyzed and estimated. This paper applies D-S evidence theory to distributed intrusion detection system for fusing information from detection centers, making clear intrusion situation, and improving the early warning capability and detection efficiency of the IDS accordingly.