In order to realize the NC precision milling of the complex aero-parts’ special structure such as large opening and closing angle chord,the technology of expanding the machine tool pendulum angle range was proposed based on change the space position of the workpiece.According to the double pendulum axis structure of the machine tool,the corresponding relationship between the compound pendulum angle of the machine tool and the pendulum angle of the axis A and axis B were established,so the compound pendulum angle range of the machine tool was studied.Based on the established kinematic model of the machine tool,the corresponding relationship between the rotation angle of the workpiece and the compound pendulum angle of the machine tool was studied,so the maximum allowable rotation angle of the workpiece in the machining plane was calculated.The results show that when the pendulum angle range of the axis A and axis B is ±25°,the maximum compound pendulum angle of the machine tool is 34.8°;when the required machining pendulum angle is between 25° and 34.8°,the five-axis milling of its special structure could be realized by rotating the workpiece;the rotation range of the workpiece decreases with the increase of the required machining pendulum angle,when the required machining pendulum angle is increased from 0° to 34.8°,the rotation range of the workpiece is gradually reduced to only 47.8°.In order to improve the clamping efficiency,a special frock was designed to realize rapid properly positioning the workpiece.