During　bolted　flange　assembly,　the　contact　stiffness　of　some　areas　of　the　joint　surface　may　be　low　due　to　the　elastic　interaction.　In　order　to　improve　the　contact　stiffness　at　the　lowest　position　of　bolted　flange,　the　correlation　model　between　the　initial　bolt　pre-tightening　force　and　the　contact　stiffness　of　bolted　flange　is　established　in　this　paper.　According　to　the　stress　distribution　model　of　a　single　bolt,　an　assumption　of　uniform　local　contact　stiffness　of　bolted　flange　is　made.　Moreover,　the　joint　surface　is　divided　into　the　compressive　stress　region　and　the　elastic　interaction　region.　Based　on　the　fractal　contact　theory,　the　relationship　model　of　contact　stiffness　and　contact　force　of　the　joint　surface　is　proposed.　Considering　the　elastic　interaction　coefficient　method,　the　correlation　model　of　the　initial　bolt　pre-tightening　force　and　the　contact　stiffness　of　bolted　flange　is　established.　This　model　can　be　employed　to　reverse　determine　the　tightening　strategy　of　the　bolt　group　according　to　working　conditions.　As　a　result,　this　provides　a　new　idea　for　the　digital　design　of　tightening　strategy　of　bolt　group　for　contact　stiffness　of　bolted　flange.　The　tightening　strategy　of　the　bolted　flange　is　optimized　by　using　the　correlation　model　of　initial　bolt　pre　-tightening　force　and　the　contact　stiffness　of　bolted　flange.　After　optimization,　the　average　contact　stiffness　of　the　joint　surface　increased　by　5%,　and　the　minimum　contact　stiffness　increased　by　6%.