Based on analyzing the existing security evaluation and forecast methods, a network security situational awareness model based on information fusion is proposed. Using D-S evidence theory to fuse multi-source network security information, this model gets the security situational values of vulnerabilities, services, hosts and network. It uses support vector regression theory to forecast future security situation in view of historical security situational values. Compared with the existing security evaluation and forecast methods, the proposed model is more integrated, effective and accurate。