Abstract: To realize the high-quality processing of wooden windows, it is necessary to study the dynamic characteristics of the spindle system of the double-ended composite finishing milling machine tool, which can provide a theoretical basis for its structure optimization and vibration reduction. A simplified three-dimensional model of the spindle system was established using the software Adams, and the cutting force and the stiffness of the spindle system supporting bearings were calculated when the milling machine processed wooden windows, and combined the software Ansys and Adams to establish a rigid-flexible coupling model of the flexible spindle, and simulated the rigid body model and the rigid-flexible coupling model of the spindle system. The X, Y, and Z vibration curves at the centroid of the spindle, cutting force action point and the pulley connection point were extracted. The simulation results showed that the X and Z direction amplitudes of the cutting force action point were the largest, and the amplitude of the centroid and the cutting force action point when the spindle was a flexible body was much smaller than when the spindle was rigid. The results of this study showed that the dynamic characteristics of the spindle as a flexible body are more in line with the actual working conditions, and the vibration curve of the three points provides a certain theoretical basis for the structural optimization of the spindle system.