The　operating　condition　of　ball　screws　is　generally　applied　to　ensure　the　ball　screws　with　a　high　transmission　efficiency　and　a　high　positioning　accuracy.　Aiming　at　the　optimal　operating　condition　of　double-nut　ball　screws,　a　transmission　efficiency　model　considering　the　kinematic　analysis　and　lubrication　status　was　proposed.　Firstly,　the　distributions　of　the　film　bearing　pressure,　asperity　bearing　pressure,　film　thickness,　and　ratio　of　the　asperity　bearing　pressure　were　determined　based　on　the　Reynolds　equation.　Subsequently,　the　transmission　efficiency　model　was　established　by　calculating　the　friction　coefficient　and　friction　torque　of　ball　screws　under　various　lubrication　statuses　and　operating　conditions.　The　optimal　operating　condition　of　double-nut　ball　screws　can　be　determined　by　estimating　the　transmission　efficiency　and　lubrication　status　to　improve　the　manufacturing　quality.　Finally,　a　friction　torque　test　based　on　the　simulated　model　was　designed　and　implemented　on　a　self-designed　bed　for　validation　of　the　proposed　model.　The　comparisons　showed　that　the　experimental　friction　torque　was　consistent　with　the　simulated　friction　torque,　which　verified　the　effectiveness　and　correctness　of　the　transmission　efficiency　model.　Results　showed　that　the　optimal　operating　conditions　of　the　entrainment　velocity　and　axial　working　load　could　ensure　high　transmission　efficiency　and　a　good　lubrication　status,　which　are　of　great　reference　to　the　green　processing　and　manufacturing　fields.