Taking into account the characteristic of the high-voltage transmission line, this paper discusses the basic principle of the eddy current testing method. Then it discusses the detection principle of eddy current of the differential coil further. 结合高压输电线的特点,在论述了电涡流检测方法的基本原理之后,进一步论述了差动式检测线圈的电涡流检测原理与方法。