Network security situational awareness（NSSA）has been a hot research spot in the network security domain.A quantification method for NSSA based on conditional random fields（CRFs）was proposed.The data of network attacks from intrusion detection system（IDS）

the hosts’vulnerabilities and the hosts’states were firstly combined as the network security factors.And then the network security threat degree was defined to quantify the risk of the whole network and classify the attacks.A diverse set of effective features were incorporated in CRFs Model.The experiments on the DARPA 2000 data set generate the explicit network security situational graph.It proves that the method introduced can represent network risk more accurate and offer a good quantification for the network security situation.