Bolted　joint　is　one　of　the　most　widely　used　connection　forms　in　various　kinds　of　engineering　applications.　However,　the　presence　of　service　torque,　which　is　generated　after　tightening　and　easily　neglected,　will　affect　the　mechanical　properties　of　bolted　joints　under　torsional　loads.　In　this　work,　the　mechanical　properties　of　bolted　joints　under　torsional　loads,　as　well　as　the　corresponding　torque　thresholds,　are　theoretically　analyzed.　Firstly,　the　torque　state　analysis　under　torsional　loads　about　the　typical　form　of　bolted　joint　is　carried　out　and　followed　by　the　bolted　joint　with　multiple　plates.　Torsional　loads　in　two　opposite　directions　along　the　thread　axis　are　considered,　namely　loosening　torsional　load　and　tightening　torsional　load.　Results　show　that　the　mechanical　properties　of　bolted　joints　exhibit　distinct　characteristics　in　different　load　directions.　Loss　of　clamping　force　and　structural　failure　may　be　induced　by　loosening　torsional　load　under　specific　circumstances.　In　contrast,　the　clamping　force　may　increase　under　tightening　torsional　load.　The　mechanical　behavior　of　bolted　joints　is　determined　by　the　friction　torque　combinations　of　various　contact　surfaces　and　the　loosening　or　tightening　torque　threshold.　Therefore,　the　torque　thresholds　can　be　used　as　performance　characterization　and　control　parameters　to　further　improve　the　mechanical　properties.