A NC reform method was given for a traditional worm wheel gear grinding machine.The PMAC motion controller and the industrial control computer were selected as the control system core,which were used to build up a closed loop with the servo motor.The electronic gearbox was used to replace the traditional worm gear,so the machining accuracy was improved.By linear interpolation,the helical gear grinding by tangential differential motion was achieved on the worm wheel grinding machine without the differential structure,which could improve the machining accuracy of the helical gear effectively.