The　components　of　machine　tools　are　mainly　fixed　and　connected　by　bolts.　The　performance　of　the　assembly　can　be　affected　by　the　dynamic　characteristics　of　the　bolted　joints.　This　paper　presents　a　nonlinear　virtual　material　method　based　on　surface　contact　stress　to　describe　the　bolted　joint　for　accurate　dynamic　performance　analysis　of　the　bolted　assembly.　Fractal　geometry　theory　is　used　to　describe　the　surface　topography.　The　elastic　modulus　and　shear　modulus　of　one　micro-contact　are　derived　based　on　fractal　contact　theory.　The　equivalent　elastic　modulus,　Poisson　ratio,　and　density　of　the　bolted　joint　can　be　obtained　through　the　weighted　mean　method.　In　order　to　obtain　the　stress　distribution,　the　contact　surface　is　assumed　flat　in　the　macro-scale,　and　the　uneven　distribution　of　contact　stress　can　be　obtained　by　the　finite　element　method　(FEM).　The　contact　surface　can　be　divided　into　several　sections,　and　the　parameters　of　a　virtual　material　layer　can　be　determined　based　on　the　mean　contact　stress.　Both　theoretical　and　experimental　results　for　a　bolted　joint　are　obtained　for　a　box-shaped　specimen　under　equal　pre-tightening　force　and　bending　moment　effect.　The　results　show　that　the　theoretical　mode　shapes　are　in　good　agreement　with　the　experimental　mode　shapes.　The　relative　errors　between　the　theoretical　and　experimental　natural　frequencies　are　less　than　4.41%,　which　indicates　that　the　present　nonlinear　virtual　material　method　is　appropriate　for　the　bolted　joint　in　modeling　CNC　machine　tools.　(C)　2015　Elsevier　Inc.　All　rights　reserved.