STEP-NC is a promising data interface for CNC, by which a comprehensive set of information regarding the product to be manufactured can be conveyed for the first time to the shop floor. In this paper, the new data model is briefly overviewed and analyzed. Then functionalities and considerations as for implementation of STEP-NC controllers are identified, followed by a conceptual framework proposed for such STEP-NC controllers for a new breed of CNC machine tools featuring autonomy and cooperation. The proposed system is constituted with a planning agent and a machining agent. The former is designed to take responsibility to cooperate with the external systems, to prepare all the data needed in machining and schedule them into unit tasks, while the latter, as one of the planning agent’s local control modules in light of an excellent combination of functionality and reliability, controls the machine tools adaptively. The working mechanism of the whole system is also introduced with an illustration of the operational flow.