During　the　service　of　bolts,　their　preload　exhibits　a　random　decreasing　trend　due　to　external　loads,　affecting　contact　stiffness　and　connection　reliability.　System　uncertainties　can　also　lead　to　preload　variations　within　the　same　group　of　bolts.　In　this　paper,　we　use　the　Wiener　process　to　model　this　preload　decrease,　incorporating　drift　and　wave　coefficients　to　capture　temporal　variability　and　system　uncertainty.　This　approach　accounts　for　monotonic　preload　reduction　and　random　fluctuations,　enabling　accurate　calculations.　By　integrating　the　time-varying　preload　uncertainty　into　the　bolted　structure＇s　contact　stiffness　model,　we　establish　a　limit　state　function　for　structural　failure　and　assess　the　reliability　of　the　bolted　connection　over　time.　©　Published　under　licence　by　IOP　Publishing　Ltd.