The invention discloses an unmanned-plane-based composite insulator hydrophobicity detector, which comprises an unmanned plane main body, a suspension frame arranged at the bottom part of the unmanned plane main body, and a spraying insulation rod suspended at the top part of the inside of the suspending frame; a first end of the spraying insulation rod is provided with a spraying head, and a second end of the spraying insulation rod is provided with a balance module; the bottom part of the suspending frame is provided with a balance assistant module, the balance module and the balance assistant module are in electric signal connection with a fly control system on the unmanned plane main body; the balance assistant module comprises a servo motor arranged on the suspending frame and connected with the fly control system through the electric signal; the output shaft of the servo motor extends out of the bottom part of the suspending frame, and the lower end part of the output shaft of the servo motor is provided with a balance rod; the end part of the balance rod is provided with a balancing weight. By using the fly control system of the unmanned plane itself, the flight gesture of the unmanned plane is sensed, thus the horizontal state of the spraying insulation rod is controlled through the common effect of the balance module and the balance assistant module, so as to achieve the purpose of eliminating the inclination inertia.