Abstract: Aerostatic spindles are widely employed in precision and ultra-precision machining. To enhance the support stiffness and operational stability of high-speed motorized spindles in ultra-precision applications, a radial bearing model and a coupled gas film-rotor model were developed in COMSOL Multiphysics for a micro-orifice-throttled aerostatic motorized spindle featuring orifice diameters smaller than 0.1 mm and no recessed pressure-equalizing cavities. The coupled effects of gas film thickness, orifice diameter, and supply pressure on load capacity and static stiffness were systematically investigated and experimentally validated. Building on this, the shaft-center trajectories at various rotational speeds were further analyzed to determine the stable operating speed range of the system. The results show that both orifice diameter and gas film thickness significantly influence the static characteristics of the radial bearing, and an optimal parameter combination exists. When the orifice diameter of the target spindle is 0.05 mm and the gas film thickness is 12 µm, load capacity and stiffness achieve their optimal balance. The gas film system maintains good stability at speeds up to 8 000 r/min. These findings provide a theoretical reference and engineering basis for the design optimization and performance enhancement of micro-orifice-throttled high-speed aerostatic motorized spindles.