With the rapid development of computer technology and communication technology, user demand more and more and with the application of computer network becoming more and more widely, its scale is becoming increasingly big. But on the other hand, there are so many network security events and the traditional single defense equipment or testing equipment has been unable to meet the demand of security; computer network is faced with severe situation of the information security. Network security situation assessment technology can reflect on the whole dynamic network security situation, and give early warning to its development trend by comprehensively considering various security factors. Therefore, the network security situation assessment model and key technology has become the hot topic of research in the field of network security.