The invention discloses a voltage secondary open-delta loop monitoring device, and relates to the field of power operation and maintenance. According to the monitoring device, each phase of a three-phase loop is additionally provided with one induction coil, the three induction coils measure the current in the loop in real time, the induction coil I, the induction coil II and the induction coil III are connected with amplifying elements respectively to amplify the current, the amplifying elements are connected with a logic judgment element, then the amplified current is displayed on a displayscreen, and an alarm threshold is set according to the current value measured in advance; and when the monitored current is lower than a certain percentage of the alarm threshold or is greater than orequivalent to 50 times of the alarm threshold, a node is closed, an alarm indicating lamp is switched on, a related signal is uploaded to a last node or a common measurement and control center through a line, so that the control center takes measures. The working efficiency of operation and maintenance staff is improved, and safe and stable operation of a transformer substation is guaranteed.