A high-speed and high-torque planetary speed-increasing extension attachment milling head structure was introduced.Without changing the spindle speed of the machine tool,the planetary speed-increasing unit was used to achieve the purpose of extending the speed of the attachment milling head.The processing requirements of high-speed and high-torque of the heavy-duty gantry boring and milling machining center are met,and the machining accuracy and efficiency of the machine tool are improved.The structure has compact structure,reasonable layout and convenient assembly.