Abstract: The development of Internet application necessitates router’s ability to support those functions such as QoS （quality of service）, network intrusion detection systems （NIDS）, measurement of traffic, accounting and billing, loading balance and control congestion etc. Although implementation of these functions varies greatly, they all need packet classification. Study shows that it is difficult to develop a fast and multi-dimension packet classification algorithm. Packet classification has become a new router bottleneck, so it attracts many researchers’ attention in recent years. Systematically discussed in this paper are technologies of packet classification, such as classification model, fields likely to be used in packet classification, standard of valuing a classification algorithm, etc. By analyzing the existing algorithm and characteristics of the classifier, the principle and approach about how to design packet classification algorithm is proposed. Finally the future of packet classification and its application are also discussed.