In this paper

starting from the concept of cross-layer perception

we treat the security situation information using multiple levels and multiple view angles of networks as source data for assessment

and establish a complete metric system of all aspects of network security situation information.Then by use of Fuzzy Analytic Hierarchy Process（FAHP）

a fuzzy consistency judgment matrix is constructed at different levels of the network security situation

and the weight of security metric within each network layer is computed.The results of the assessment of network security situation are divided into five levels indicating the security of network.Finally

by the D-S evidence theory

Dempster combination rules（DCR） are acted on the assessment results of the network layer

so that we gain the results of security situation assessment of the overall network.The overall cross-layer evaluation process solves the problem of simplicity and the one-sidedness of data source

the hierarchical evaluation way speeds up the calculation

the usage of various assessment algorithm makes up the lack of each other

and the results could present the security situation information of network more accurate and comprehensive.