With the rapid development of network technologies, the expansion of network scale, and the increasing complexity of network structures, numerous challenges have emerged in the assessment of network security situations. In the field of network security, constructing a comprehensive and objective assessment index system is the prerequisite for evaluating network security situations. However, most existing security assessment methods are designed for specific scenarios, lacking global perspective and completeness. Additionally, the subjective selection of index limits the accuracy of the assessment results. This paper adopts the concept of sub-domain and proposes a method for constructing a network security situation assessment index system. This method constructs separate assessment index systems for the network domain and behavioral domain, which not only reflect the security status of network operations but also describe the security of user behavior. It addresses the limitations of existing assessment index systems that lack comprehensiveness. Finally, experimental results based on real network environment data demonstrate that the proposed method effectively reflects changes in network situation and has both practical and theoretical significance.