Abstract: Based on the finite element analysis, a magnetic leakage detection model was constructed in the article, combined with the principle of three-axis sensor for magnetic leakage detection in the actual pipeline, and the spatial distribution characteristics of the leakage magnetic field of the defects were obtained by studying the leakage magnetic signals of the flat-bottomed hole and the rectangular groove defects in the three directions of axial, radial and circumferential directions. It was found that the triaxial signal of leakage magnetic field reflected the shape profile of flat bottom hole more than rectangular slot; for flat bottom hole defects, different chord lengths could reflect the signal change characteristics of triaxial to a certain extent, which was verified through experiments, and it had certain engineering guiding significance for a variety of defects identification and quantitative assessment.