The invention provides a numerical control machine tool processing performance monitoring system which is characterized in that monitoring devices on a plurality of machine tools are connected with each other by Ethernet network by a management server; the monitoring device receives the data of the self-state of the machine tool, collects the current of a mainshaft motor and a feeding motor and the vibration quantity of a mainshaft, processes the collected data, compares the processing result with the judgment standard of the machine tool processing performance, emits control instructions to control the processing process according to the given control strategy, and feeds back all relevant information to the management server; the management server analyses the processing performance state and the development trend of the machine tool. The system carries out monitoring to the self-parameters and the in-situ processing state of a plurality of the machine tools, analyses the current processing performance the development trend of the machine tool, and self-adaptively controls the complex processing process, thus effectively ensuring the processing safety and quality.