The chaotic oscillator detection method applies the bifurcation characteristic of the driven Duffing oscillator to detect signals. The chaotic system is sensitive to certain signals and immune to noises， thus the performance is propitious to the detection sensitivity and anti-interference capability. A new method for the monitoring system of arcing fault is therefore proposed. The weak signals before arcing fault， annihilated by strong noise， are available and then the Duffing oscillator signal detection is added as the periodic disturbing force. If the monitoring system is on conditions of intermittent chaos， which proves existence of arcing sound， the arcing sound will be operated as early warning. If the arcing light and current occur simultaneously， the monitoring system will then send out warning signals of arcing fault. The system fulfills on-line detection of arcing fault and the warning and early warning are established with the arcing sound， arcing light and short-circuit current. The system， furthermore， has been proved with high accuracy and quickness in terms of the experimental results.