Establishing　the　normal　equivalent　properties　model　of　bolted　joints　by　boundary　condition,　the　equilibrium　and　compatibility　conditions.　Then　obtain　the　first　two　natural　frequencies　and　damping　ratio　by　modal　testing　under　the　different　preload,　and　identification　the　relationship　between　different　preload　and　equivalent　stiffness　and　damping　of　bolted　joints.　Finally,　establishing　the　finite　element　model　of　including　bolted　joints　by　ANSYS　soft　and　obtain　the　first　natural　frequencies　and　damping　ratio,　the　error　between　the　theoretical　and　experimental　results　of　the　model　is　less　than　4.73%,　it　can　be　show　the　validity　and　feasibility　of　the　proposed　method.　Besides,　the　studied　results　show　that,　in　the　test　range　of　this　paper,　the　stiffness　and　damping　coefficient　of　the　joint　surfaces　increase　with　the　preload,　and　further　proved　the　dynamic　properties　of　a　mechanical　system　are　strong　affected　by　the　properties　of　bolted　joints,　especially　in　the　case　of　the　low　preload.