Numerical control transformation for CGM6125 machine tool was made based on open CNC system. In mechanical structure, the original transmission mode of each axis was changed, the new transmission scheme was designed. In control system, the designed scheme was “motion controller +PC”, the control function was accomplished by industrial PC, the motion signal was sent to driver by motion controller, the driver controlled the speed and movement of the motor according to the feedback, so the movement of each axis was controlled. In humanmachine interaction, the soft and hardware structure were established, through the programming on the interface functions, the application program of open CNC system was built based on Delphi platform. The CNC functions of machine tool were realized.