STEP-NC is a new CAM/CNC interface and an extension of STEP into numerical control machining. It has been partly formed into draft international standard (ISO 14649) and is expected to replace ISO 6983 in the near future. In the first section of this paper, the STEP-NC data model is analyzed and those parts that are relevant to NC milling process are abstracted. Then issues involved in NC part machining based on STEP-NC paradigm are discussed including NC programming and the machine control. Based on the analysis, a prototype system is outlined and partly developed with libraries and software tools in ST-Developer environment to interpret the part program into internal data format and to assist the shop floor level planning. Finally the user interface of this system is introduced.