On the basis of the movement characteristics of the helical milling endeffector, a design scheme of the open motion control system for the endeffector was presented based on PC and motor control card of DMC5480. The hardware platform was set up with PC as the core of the motion control processor, and the motion card DMC5480 as motion controller. The software platform which has the characteristics of openness, universality and flexibility was exploited by Visual Basic. The test device of the open control system was built to verify the reliability of the endeffector control system based on the software and hardware platform.