Abstract: Stealing oil by hole-drilling in long-distance pipelines is increasingly specialized and highly concealed, which has become a major challenge in the integrity management of pipeline enterprises. Aiming to overcome the shortcomings of conventional detection methods, such as low detection rate, high cost and long period, a special internal detector for anti hole-drilling type oil theft based on eddy current principle was developed. The basic principle of eddy current inner detection, the mechanical system and electronic hardware system of inner detector were expounded, and the analysis of hole-drilling type oil theft inner detection data and the identification of characteristic signals were studied. The results of pulling test, field application and excavation verification show that the in-line detector for hole drilling type oil theft can effectively detect and accurately locate the theft point, and at the same time, it can also detect some typical inner wall defects, thus reducing economic losses and secondary hazards caused by them.