The　self-loosening　of　high　strength　bolt　caused　by　vibration　has　been　widely　studied.　However,　the　short-term　self-loosening　behavior　of　the　high　strength　bolt　when　it　is　not　subject　to　an　external　load　has　not　received　attention.　This　behavior　will　also　lead　the　bolt　preload　to　attenuate.　Since　the　theoretical　analysis　of　self-loosening　behavior　is　difficult,　this　paper　uses　the　finite　element　method　to　construct　an　accurate　three-dimensions　model　with　thread　lift　angle　for　numerical　analysis.　A　new　method　is　proposed　to　analyze　the　self-loosening　behavior.　The　self-loosening　behavior　caused　by　the　elasticity　and　plasticity　of　the　bolted　joint　at　different　deformation　periods　is　compared　and　analyzed.　Besides,　the　evolution　of　the　self-loosening　behavior　under　different　conditions　is　explored.　The　analysis　results　show　that　the　torsional　deformation　of　the　thread　leads　to　the　relative　slip　of　the　internal　and　external　threads.　This　results　in　the　self-loosening　of　the　thread　in　the　elastic　condition.　In　the　elastic-plastic　deformation　condition,　the　self-loosening　behavior　is　caused　by　the　relative　slip　of　the　internal　and　external　threads　and　plastic　deformation.　The　weight　of　plastic　deformation　is　greater.　In　addition,　this　behavior　has　the　characteristics　of　increasing　with　increased　tightening　torque　and　decreasing　with　increased　friction　coefficient.