The invention provides a PLC-based numerical control milling machine pneumatic control system. The component parts of the control system comprise a PLC, a frequency converter, an electric reactor, a compressor, a motor, a pressure transmitter, a contactor, an air switch, an intermediate relay, a voltmeter, an ammeter, a cable, etc. According to the control system, clamping operation of the millingcutter is completed by using PLC control so that the degree of automation of control can be enhanced and the performance of the numerical control milling machine can be enhanced. According to the control system, the energy can be saved, vibration can be reduced, the service life of the system can be prolonged and the maintenance cost can be reduced.