Aiming at the weakness of being unable to provide numerical value of risk and avoid jamming encountered in the current security evaluation system

this paper presents a quantitative model of network security risk assess system

which is based on fuzzy algorithm and hierarchy.This model firstly establishes logical hierarchy of network

viz.service

host and whole network system

and calculates the risk value of service by putting forward the corresponding computation method of asset

threat and vulnerability

then adopts fuzzy algorithm to educe the risk value of every layer.This model evaluates security factors from bottom to top and gives the intuitionistic security situation from local to global.The experiments on the historical dataset show that applying this model can accurately describe network security status in three hierarchies.