The fixture of motorized spindle plays a definitive role in clamping stability and working reliability. If designed irrationally, not only will affect the precision of the micro-milling machines, but also cause the spindle drop. Based on the phenomenon that the spindle drops at high-speed in micro-milling process, this paper optimized the existing fixture, designed the supporting protective device, and analyzed their static characteristics utilizing ANSYS finite element analysis software. To guarantee the sufficient strength of bolts on the fixture and the protective device, both the theory analysis method and ANSYS finite element analysis method are used to make the strength check of the selected bolts. The optimization of the fixture for high speed motorized spindle has far-reaching affect on the design of high-speed motorized spindle.