Bolted　joints　are　elements　used　to　create　resistant　assemblies　in　the　mechanical　system,　whose　overall　performance　is　greatly　affected　by　joints＇　contact　stiffness.　Most　of　the　researches　on　contact　stiffness　are　based　on　certainty　theory　whereas　in　real　applications　the　uncertainty　characterizes　the　parameters　such　as　fractal　dimension　D　and　fractal　roughness　parameter　G.　This　article　presents　an　interval　estimation　theory　to　obtain　the　stiffness　of　bolted　joints　affected　by　uncertain　parameters.　Topography　of　the　contact　surface　is　fractal　featured　and　determined　by　fractal　parameters.　Joint　stiffness　model　is　built　based　on　the　fractal　geometry　theory　and　contact　mechanics.　Topography　of　the　contact　surface　of　bolted　joints　is　measured　to　obtain　the　interval　of　uncertain　fractal　parameters.　Equations　with　interval　parameters　are　solved　to　acquire　the　interval　of　contact　stiffness　using　the　Chebyshev　interval　method.　The　relationship　between　the　interval　of　contact　stiffness　and　the　uncertain　parameters,　that　is,　fractal　dimension　D,　fractal　roughness　parameter　G,　and　normal　pressure,　can　be　obtained.　The　presented　model　can　be　used　to　estimate　the　interval　of　stiffness　for　bolted　joints　in　the　mechanical　systems.　The　results　can　provide　theoretical　reference　for　the　reliability　design　of　bolted　joints.