In this paper, Data model used in intelligent CNC system based on STEP-NC is presented. A multi-agent architecture of the intelligent CNC system based on STEP-NC is proposed. The architecture consists of fourteen functional agents, such as interpreter agent, process planning agent, simulation agent, tool path planning agent, monitoring agent, expert system agent, etc. Some key technologies to implement the intelligent control including simulation, online inspection and expert system are discussed detailed. As a result, the architecture and key technologies proposed in this paper will aid the development work of the intelligent STEP-NC system.