This paper aimed at NC system’s high-speed, high-accuracy, high reliability requirements. The condition monitoring, faint information extraction and fault diagnosis technology are researched of complex CNC system. Elaborated to develop a common interface and achieved the seamless interaction of CNC system and reconfigurable embedded monitoring unit basis. A machine tool monitoring diagnostic verification platform with on-machine monitoring and intelligent maintenance features of CNC system is constructed based on the internet. Integration achieved the CNC machine tools’ status remote monitoring and fault diagnosis, and detailed analysis of the key technologies for the components of the system. Through effectively integration of the computer technology, weak signal extraction technology, fault diagnosis or other technologies to enhance the automation, networking and intelligent level of the complex CNC system.