Ball　screw　mechanism　(BSM)　plays　a　key　role　to　transmit　motion　and　power　in　a　machine　tool.　The　accuracy　of　the　machine　tool　is　greatly　influenced　by　the　accuracy　of　the　BSM.　Since　accuracy　degradation　of　BSM　is　primarily　due　to　wear,　the　wear　behavior　of　BSM　is　studied　considering　the　time-varying　motion　and　loading　working　conditions.　A　new　wear　prediction　model　of　BSM　is　introduced　in　this　research　considering　complex　working　conditions.　Because　BSM　is　subject　to　dynamic　fluctuations　of　rotational　speed　and　loading　in　the　operation　process,　a　loading　model　is　established　to　describe　the　dynamic　contact　force　between　the　ball　and　the　raceway,　and　a　motion　model　is　developed　to　describe　the　dynamic　sliding　and　rolling　behaviors　between　the　ball　and　the　raceway.　The　degradation　of　BSM　accuracy　is　analyzed　considering　time-varying　motion　and　loading　working　conditions.　Experiments　have　also　been　designed　and　conducted　to　demonstrate　the　effectiveness　of　the　accuracy　degradation　analysis　for　BSM.　Crown　Copyright　(C)　2018　Published　by　Elsevier　Ltd.　All　rights　reserved.