The　bolted　joint　provides　more　than　half　of　the　stiffness　and　nearly　all　of　the　damping　of　the　whole　machine　tool.　It　is　necessary　to　study　the　dynamics　mechanism　and　establish　accurate　model　of　joint　surface.　The　paper　proposes　the　model　of　nonlinear　virtual　material　based　on　fractal　theory　and　Hertz　contact　theory,　the　contact　surface　can　be　divided　into　several　sections　based　on　the　pressure　distribution,　the　elastic　modulus　and　stress　of　each　section　can　be　calculated.　An　L-shaped　specimen　is　designed　to　validate　the　accuracy　of　presented　model.　The　maximum　errors　of　natural　frequencies　between　theoretical　and　experimental　is　8.8%,　suggesting　that　nonlinear　virtual　material　method　is　appropriate　for　the　bolted　joint.