Aim at the communication problems of computer and NC machine tool, a practical DNC system is developed in this paper. A three-layer control structure mode – which is composed by the unit layer, DNC computer workstation layer and NC system equipment layer – is presented. Based on its good real-time capability and high reliability, CAN field-bus is introduced into the DNC communication system construction, the network topology is constructed and related hardware is chosen properly. Using VC++6.0 as development tool, and assisted with special compiling tools LEX&YACC, 3D standard graphic library OpenGL and database Microsoft Access, and based on the multi-task and multi-thread technologies, the software of the system is developed. The system has the characteristics of reliable operation, simple structure and high real-time capability, can improve the efficiency of NC machining process obviously, and has a certain application prospect in the middle and small scale manufacturing enterprises of our country.