The open computer numercial control (CNC) system of PC + I/O architecture was researched and strong realtime tasks in CNC systems were realized with software algorithms. Modular method was adopted to establish the software architecture of the system. The grinder CNC system software development method in the Windows + RTX software platform was discussed. Automatic programming module was designed by combined with the plate cam CNC grinding algorithms. The interpolation algorithm is researched based on the plate cam grinder. The realtime network control module was designed by using RTTCP/IP protocol. The grinding experiment verifies that the CNC system has high accuracy, fast response and good stability, and can absolutely satisfy the performance requirement of the grinder.