To　determine　the　thermal　deformation　of　ball　screw　in　actual　working　condition,　a　novel　method　for　determining　thermal　deformation　of　ball　screws　in　complicated　working　condition　is　proposed　based　on　G-code　and　finite-element　(FE)　method.　In　the　complicated　working　condition,　it　is　difficult　to　obtain　and　import　the　nut　movement　into　FE　model　due　to　the　complex　nut　movement.　In　this　research,　the　nut　movement　is　directly　determined　from　G-code　by　MATLAB　code　programming.　The　nut　location　is　recorded　with　time　in　a　file.　The　thermal　parameters　can　be　determined　according　to　the　nut　speed　with　time　as　well.　In　the　implicit　FE　analysis,　the　nut　location　is　read　from　the　input　file　instead　of　nut　location　calculation　before　every　time　step.　And　then,　the　effect　of　factors,　such　as　working　condition　and　materials,　on　thermal　deformation　reduction　of　ball　screw　is　studied.　The　thermal　deformation　reduction　of　ball　screws　under　different　rotational　speed,　actual　working　condition,　and　different　axial　elastic　modulus　of　composites　is　discussed,　which　can　provide　the　guidelines　to　evaluate　the　thermal　deformation　reduction　and　design　the　composite　in　improved　ball　screws.