Due to the influence of the acid rain, salt spray and ice hazard, the hydrophobicity of composite insulators would be reduced gradually. It is necessary to detect the hydrophobicity of insulators regularly. The periodic detections of insulators are difficult due to the problems as the long operation time, high labor intensity and high risk coefficients. Therefore, a hydrophobicity detection method of composite insulators based on the multirotor UAV (unmanned aerial vehicle) is proposed and the corresponding device is also developed in this paper. The device is composed by a sixrotor UAV, an automatic water spray system, a wireless remote control system, a video capture transmission system and a hydrophobicity detection system. The live working is carried out by controlling the DC microelectronic diaphragm pump to generate adjustable diffused water to spray on the target composite insulator evenly. During this process, the visual mode function of camera can be employed to assist the spraying operation. Then, photos of the target composite insulator are taken by the camera and then transmitted for hydrophobicity analysis. Finally, a test is included for verification. It is shown that the method and device have the advantages of automation, unmanned and remoteness in the whole detection process. The safety of operators can be guaranteed, and the hydrophobicity of composite insulators can be detected accurately.