Aiming at the characteristics of modularity and reconfigurable in open architecture computer numerical control (CNC) system, the open architecture CNC system, Harbin Institute of Technology computer numerical control (HITCNC), is researched and manufactured based on the interface standards. The system’s extal interfaces are coincident with the corresponding intational standards, and the intal interfaces follow the open modular architecture controller (OMAC) agreement.In the research and manufacturing process, object-oriented technology is used to ensure thc openness of the HITCNC, and static programming is applied in the CNC system according to the idea of modularization disassembly. The HITCNC also actualizes real-time and unreal-time modules adopting real-time dynamical linked library (RTDLL) and component object model (COM). Finite state machine (FSM) is adopted to do dynamically modeling of HITCNC. The complete separation between the software and the hardware is achieved in the HITCNC by applying the SoftSERCANS technique.The application of the above key techniques decreases the programming workload greatly, and uses software programs replacing hardware functions, which offers plenty technique ensures for the openness of HITCNC. Finally, based on the HITCNC, a three-dimensional milling system is established.On the system, series experiments are done to validate the expandability and interchangeability of HITCNC. The results of the experiments show that the established open architecture CNC system HITCNC is correct and feasible, and has good openness.