The utility model relates to a gauge, and specifically relates to a capacitor bank fault detector comprising a power supply module, and a control module, a detection module, a storage module and a display all connected with an output end of the power supply module; an input end of the detection module is connected with a detection port connecting with a to-be detected capacitor bank; the detection port comprises a built-in current transformer sampling lead-in end, a built-in current transformer sampling lead-out end, a test line voltage sampling input end, an external current clamp wire lead-in end, and a discharge coil secondary side connecting end; an input end of the control module is connected with an output end of the detection module and a setting keyboard; the control module processes detection data from the detection module according to control parameters inputted by the setting keyboard, thus outputting measuring result on the display. The capacitor bank fault detector can measure a single single-phase capacitor of grouped paralleled capacitors without dismounting a wire, and can measure three-phase capacitors of various connection types; the capacitor bank fault detector is simple in usage, and high in detection efficiency.