The performance of the high-speed motorized spindle strongly affects the performance of the high-speed CNC machine tool. To improve the MTBF level of a high-speed CNC machine tool, it is of great importance simulating the real working condition of the motorized spindle and developing a reliability test platform. In this paper, a reliability test platform for high-speed motorized spindles is designed based on power dynamometer and piezoelectric loading systems. The reliability test of the motorized spindle can be carried out with a rotation speed over 18000r/min; the performance indices of the high-speed motorized spindle can be determined, such as the performance of the temperature rising control, the radial runout and the axial play of the motorized spindle; with the power dynamometer and piezoelectric loading systems, the loading condition of the spindle can be simulated, including the radial force, the axial force and the torque, and the dynamical loading test of the motorized spindle can be carried out; the failures during the test can be detected; the information of the test can be recorded, and the reliability analysis can be made according to the data collected from the test, providing a quantitative evaluation platform for improving the reliability of the motorized spindle.