According to the recognition of the fault of the transmission line, the traditional methods of manual detection, image recognition and infrared observation can not distinguish the defects, but the line produces the electromagnetic interference level change is its produces the flaw the important characteristic. Therefore, the electromagnetic interference (EMI) can be used as a parameter in the inspection of high-voltage transmission line. this paper studies the correlation between the fault of the transmission line and the distribution of the high frequency electromagnetic spectrum, by analyzing the level change of the electromagnetic interference between the normal wire and the broken wire, the defects such as the old wire, the broken wire and the serious corrosion, which can not be distinguished by image, are detected, it provides a strong technical support for the condition assessment of transmission line conductors.