s：The hydrophobicity of composite insulators on-line detecting device based on the collection of a variety of advanced technology as a whole,including digital image processing technology, computer software technology and the remote wireless signal control and transmission technology. Install it to the composite insulator need regular monitoring after each detection, can realize the automation process, avoid each previous measurement by manual operation and a plethora of human errors. By using the device and spray method respectively in three groups of composite insulator hydrophobicity rank test,the results of two methods are completely consistent, proved the accuracy and reliability of the device measurement. Since the device is developed, through on-line hydrophobicity detection regularly for 5 months, analysis of the data and draw relevant conclusions, finally prospected. The device can make the power workers to master the operation of composite insulator hydrophobic condition, provide accurate and effective basis for condition based maintenance of transmission line.