The invention provides a FANUC numerical control system I/O module detector and belongs to the technical field of the detecting and maintaining of numerical control systems. The I/O module detector includes a switch power supply, an intelligent processor, an encoder, a soft keyboard board desk, an I/O adapter plate, a LCD display and an I/O module. The intelligent processor has a display control signal output end which is connected to a control signal input end of the LCD display. The switch power supply has voltage divided through a first resistor R1 and a second resistor R2, then forms a stable 5V voltage through a voltage-stabilizing tube for supplying power to the intelligent processor and the soft keyboard board desk. The soft keyboard board desk has a signal output end which is connected to a signal input end of the LEC display. The signal input end and the signal output end of the LCD display and a signal output end of the I/O module are all connected to a signal input end of a FANUC system through a 50 flexible printed circuit. The detector has strong anti-interference capability and can respond quickly.