Abstract: Attack detection is an important approach to enhancing computer system security. The study of attack classification has a significant role to analyze computer system vulnerability and technique used for attack and can help to build effective detection methods. A detection-oriented network attack classification approach—ESTQ is introduced and analyzed using formal description technique. Based on ESTQ classification approach, a network intrusion detection method is built and a distributed network intrusion detection system—DNIDS is designed. Finally, a DNIDS prototype system is implemented.