Abstract: Taking the German NILES ZP08 gear profile grinding machine CNC system installed in 2001 as an example, the old D300 CNC system machine tool of the original equipment was upgraded to the domestic mainstream Siemens 840D sl CNC system, which verified the feasibility of upgrading the CNC system of the old imported equipment, and provided a reference for the technological upgrading of related enterprises. The CNC system upgrading plan mainly focuses on the electrical control of the machine tool and the restoration of mechanical accuracy. The electrical part upgrades the CNC system for the equipment, and the users can choose the gear grinding process according to the production needs through combining various software packages written and developed based on the new CNC system. The mechanical accuracy recovery section restores the accuracy of each axis that affects the machining accuracy of the machine tool, and carries out fault maintenance of peripheral auxiliary equipment. After completion of the transformation, the machining accuracy of the equipment has been improved and the failure rate has been greatly reduced. Through the success of this upgrade, it provides a new idea and method for upgrading of the old equipment system in China, and also reduces the operating costs of enterprises.