The invention discloses a special-purpose instrument for live-line detection on an insulator. The special-purpose instrument comprises an operation insulation rod (1), an insulation board (2), two voltage sensors (3) and a single-chip microcomputer (4), wherein one side of the insulation board (2) is connected with two detection electrodes (5), the other side of the insulation board (2) is connected with the operation insulation rod (1) through a universal joint assembly, the two voltage sensors (3) are mounted on the insulation board (2), head portions of the two detection electrodes (5) are connected with two sides of the insulator, and tail portions of the two detection electrodes (5) are respectively connected with voltage input interfaces (7) of the single-chip microcomputer (4) through the two voltage sensors (3) and two connection wires (6).