With the continuous development of modern network information technology, the traditional passive network security defences are static defences that can not effectively respond to new types of network threats and can no longer meet the needs of network security. As the main network defence mean, active defence overcomes the many defects of traditional defence, can effectively respond to unknown network activities, showing strong advantages. Starting from the development process of active defense, the main technologies currently existing in network security active defense were sorted out, and the advantages and disadvantages of the main technologies at four levels, namely, network security intrusion defence, network security intrusion detection, network security intrusion prediction, and network security intrusion response, were summarised and analyzed, as well as the analysis and outlook of its future development direction.