Elastic　connection　of　spindle-tool　holder　is　one　of　the　weak　points　of　spindle　systems.　It　directly　affects　dynamic　characteristics　of　machining　system.　Stiffness　modeling　of　spindle-tool　holder　is　the　key　problem　in　dynamic　analysis　of　spindle　system.　Considering　the　influence　of　cutting　force,　an　analytical　method　combining　classic　elasticity　theory　with　fractal　theory　is　proposed　to　estimate　the　contact　stiffness　at　the　spindle-tool　holder　interface.　The　effectiveness　of　the　proposed　method　is　validated　by　self-designed　experiment.　An　approximate　model　is　proposed　to　replace　finite　element　model　in　the　processing　of　identification　of　contact　stiffness　of　spindle-tool　holder　in　order　to　save　calculation　time.　On　that　basis,　effects　of　cutting　force　on　contact　stiffness　of　spindle-tool　holder　are　investigated　in　this　article.　The　conclusion　can　be　drawn　that　cutting　force　has　great　effect　on　stiffness　of　spindle-tool　holder.　Contact　stiffness　of　spindle-tool　holder　can　be　obtained　by　the　method　proposed　in　this　research　on　the　premise　of　not　making　prototypes　or　utilizing　hammer-hitting　pulse-inspirit　method.　The　calculating　model　and　method　in　this　article　can　be　implemented　to　solve　the　contact　stiffness　at　the　spindle-tool　holder　during　the　design　stage.