Abstract: The underline foreign objects is a common defect for transmission line. When foreign objects is under the transmission line, there will be plants and other foreign objects which affect the normal operation of the transmission line. It will cause a large accident if we do not deal with that in time. Therefore, how to prevent accidents such as bulging under the line has become the top priority of the research. This paper studies and designs an intelligent inspection robot for a line of foreign objects. Through the high-definition camera of the inspection robot, the image of the detection area is collected. The Digital Signal Processor (DSP) chip is used to preprocess it in real time, and the virtual wire frame technique is used to mark a region in the image range. The threshold value changes are monitored in real time to get the distance between the transmission line and the foreign objects under the line. If the test result is abnormal, the image will be compressed to JPEG format and sent to the monitoring technician for alarm.