Bolted　connection　is　one　of　the　most　widely　used　connection　forms　in　various　mechanical　structures.　However,　the　discretization　of　preload　during　tightening　will　be　aggravated　by　the　presence　of　geometric　error　caused　by　manufacturing.　In　this　work,　the　geometric　error　transmitted　by　all　parts　of　the　bolted　joint　is　equated　to　the　existence　of　a　certain　wedge　angle　between　the　nut　and　the　bearing　surface　of　the　connected　part,　that　is,　the　nut　and　the　bearing　surface　are　in　non-parallel　contact.　A　torque-preload　mathematical　equation　is　theoretically　established　to　account　for　non-parallel　contact.　On　this　basis,　the　relation　between　torque　and　preload　deviation　is　considered　to　analyze　the　formation　mechanism　of　preload　deviation　according　to　non-parallel　contact.　Subsequently,　the　influence　of　non-parallel　contact　on　tightening　performance　was　quantitatively　analyzed　by　experiments　and　finite　element.　The　analysis　results　showed　that　the　tightening　process　under　non-parallel　contact　can　be　divided　into　two　stages:　nonlinear　increase　stage　and　linear　increase　stage.　Among　them,　the　deviation　mainly　appears　in　the　first　stage.　Tightening　performance　analysis　herein　is　helpful　to　reduce　the　influence　of　geometric　error　on　the　preload　control　and　further　improve　its　reliability.