The　spindle　shaft　of　heavy　load　deflection　angle　milling　head　is　an　important　functional　component　of　5-axis　CNC　machine　tool,　which　has　characteristics　of　high　torque　and　high　power,　used　for　large　and　complex　free-form　surface　processing.　The　spindle　shaft　is　modeled　as　Timoshenko＇s　beam　by　including　the　centrifugal　force　and　gyroscopic　effects.　The　effects　on　inherent　characteristic　of　the　spindle　shaft　of　heavy　load　deflection　angle　milling　head　are　analyzed　owing　to　axial　force　and　spindle　shaft　speed.　Simultaneously,　numerical　solution　of　spindle　shaft　is　gotten.　And,　the　numerical　results　are　well　agree　with　the　exact　modeling,　which　illustrates　that　the　theoretical　modeling　of　spindle　shaft　is　correct　and　the　exact　dynamic　characteristics　of　spindle　shaft　is　obtained.　The　analytical　modeling　results　of　spindle　shaft　are　effective　and　helpful　for　design　and　improvement　of　spindle　shaft　of　heavy　load　deflection　angle　milling　head.