Computer numerical control (CNC) machine tools are now moving toward high precision, high speed, and complex functional machining. Machining monitoring system is important to achieve intelligent control of machining process to produce complex geometric features and precision parts. Traditional NC machining monitoring system is limited in data features, low in adaptability, and slow in transmission efficiency, and hard to achieve intelligent online assessment. To overcome these difficulties, this study proposes a smart monitoring system for CNC machining based on Cyber-Physical Production System (CPPS) framework. It is built on the CNC machine tool physical and virtual modeling, process monitoring, and big data analytics, and then synergized into a system through a distributed network. Under the CPPS framework, the smartmonitoring system is divided into control layer, network layer, and decision layer. The function of each layer and the key technologies of the CPPS involved are discussed. Case studies of machining process monitoring are studied in the applications.