This　paper　presents　a　method　of　predicting　the　radial　rotary　error　of　an　aerostatic　spindle　based　on　the　microscale-effect　to　investigate　the　influence　of　gas　film　fluctuation　on　the　rotation　accuracy　of　the　aerostatic　spindle.　First,　the　gas　bearing　of　the　spindle　is　simplified　as　a　spring-damping　system　with　two　degrees　of　freedom　perpendicular　to　each　other.　Additionally,　the　aerostatic　spindle　bearing-rotor　system　is　established　by　considering　the　forced　vibration　and　deflection　vibration　of　the　rotor.　Subsequently,　the　microscale-effect　is　introduced　into　the　dynamic　model　of　the　gas　film　flow,　and　the　dynamic　Reynolds　equation　of　the　gas　film　is　established　in　the　microscale.　Moreover,　the　nonlinear　dynamic　stiffness　and　dynamic　damping　coefficient　are　obtained　by　the　perturbation　method.　The　nonlinear　dynamic　parameters　in　the　microscale　are　introduced　into　the　dynamic　model　of　the　bearing-rotor　system　and　all　the　vibration　errors　are　obtained.　By　comparison　with　the　conventional　case,　it　is　found　that　the　spindle　gyration　error　increased　and　that　the　response　delay　occurred　when　the　microscale-effect　is　considered.　Moreover,　the　influence　of　the　supply　pressure　and　speed　on　the　vibration　of　the　spindle　is　also　analyzed.　An　experiment　measuring　the　spindle　rotation　error　is　carried　out.　The　experimental　results　reveal　that　the　prediction　method　of　the　nonlinear　spindle　rotation　error　in　the　microscale　is　more　accurate,　and　that　the　errors　are　5.8%　and　9.6%.