Bolted　joints　have　a　significant　effect　on　the　dynamical　behaviour　of　assembled　structures.　Accurate　contact　stiffness　model　of　bolted　joint　is　crucial　in　predicting　the　dynamic　performance　of　bolted　structures.　In　this　research,　a　modified　three-dimensional　fractal　model　of　normal　contact　stiffness　is　presented　to　more　accurately　predict　the　dynamic　characteristic　of　a　bolted　assembly.　In　the　present　model,　while　the　contact　deformation　exceed　the　critical　value　the　elastic-plastic　contact　is　used　to　take　the　place　of　Hertz　elastic　contact　in　the　traditional　M-B　model,　and　revise　the　drawback　that　elastic-plastic　contact　occurs　before　elastic　contact　in　existing　elastic-plastic　fractal　models.　As　the　increase　of　contact　force,　the　plastic　deformation　of　single　asperity　is　considered　again,　which　is　omitted　in　the　two　type　fractal　models.　An　experimental　set-up　with　two　T-shaped　specimen　is　designed　conducted　to　verify　the　efficiency　of　the　proposed　model.　Comparing　with　the　ZX　elastic-plastic　fractal　model,　the　present　model　can　predict　contact　stiffness　and　dynamic　performance　more　accurately,　particularly,　while　for　higher　contact　loads.　The　results　show　that　the　modified　elastic-plastic　fractal　contact　model　can　be　used　to　more　accurately　predict　the　stiffness　and　dynamic　characteristic　of　bolted　structures　in　the　machine　tools.　©　Published　under　licence　by　IOP　Publishing　Ltd.