Abstract: In view of problem that existing feed state sensor is susceptible to external electromagnetic interference and leads to inaccuracy monitoring results, and cannot monitor power-down state of AC3 300 V and above equipments, detection principle of non-contact capacitive electric field was studied, and two kinds of structure forms of sensing head of feed state sensor were designed to detect electric field change of armored cable and unarmored cable, so as to achieve online feed monitoring of controlled equipment, and effectively solves problems of misinformation, poor anti-interference ability and poor stability of existing mine-used feed state sensor while detecting unarmored cable.