Abstract: The unmanned aerial vehicle（UAV）for power transmission line inspection can improve the efficiency and precision of inspection and save the operation cost. The hardware equipment of transmission line inspection system is composed of laser ranging radar and infrared imaging equipment on the UAV. Based on the rapid expansion of random tree calculation, the algorithm of radar obstacle avoidance is developed. The method of histogram equalization is used to process the infrared image of the system, and the UAV inspection control system is developed on the Android operating system.The application results show that the UAV can automatically avoid the line obstacles during the inspection, and the line defects can be clearly seen by the inspection image which proves the effectiveness and feasibility of the inspection method.