Abstract: Network security situation assessment process has a large number of complex and uncertain influence factors．Aiming at the problem of lack of correctness and rationality in situation assessment,the situation index identification space and evaluation criteria based on the DS evidential theory were set up．The network situation assessment method based on DS and Knowledge Fusion was proposed through expert knowledge fusion reasoning,and the situation assessment case analysis was verified,combining the computation of three-layer network host vulnerability index．Experimental results show that the method has good effect in situation assessment,and thus provides a feasible solution for situation assessment.

Key words: Network security,Situation assessment,DS evidential theory,Situation entropy,Vulnerability