Abstract: Aiming at the shortage of the retracting movement of the main shaft of the sliding part milling head of the common part of the combined machine tool, a structural scheme of the retracting movement of the main shaft driven by the servo electric cylinder is designed. The milling head spindle is extended and retracted into a linear reciprocating motion. The hydraulic cylinder drive is converted into a servo electric cylinder push rod drive. The spindle extension position is stepless and precise control, and has the functions of automatic rough milling, semi-finishing milling, finishing milling and allowing the knife. Flexible machining on CNC combined milling machines has been widely used.