Magnetic flux leakage detection is widely used in the defect detection of ferromagnetic materials because of its convenient operation, low requirement of detection environment and high automation. However, the pathology of irregular defect leakage reconstruction leads to low accurate reconstruction results, especially the magnetic leakage reconstruction of 3D irregular defects. Therefore, the 3D defect reconstruction problem is transformed into the 2D defect reconstruction one in this study. A forward model based on coordinate offset magnetic dipole is proposed, which can quickly and accurately calculate the magnetic leakage signal of arbitrary complex defects, and the Newton-Raphson method is used to reconstruct three-dimensional irregular defects. The simulation and experimental results show that compared with the Levenberg-Marquardt reconstruction algorithm, the proposed reconstruction algorithm provides obvious accuracy improvement by reducing the average reconstruction errors of 41% , and average maximum depth errors of 62% , which realizes the rapid reconstruction of 3D irregular defects. Keywords:magnetic leakage detection; defect reconstruction; magnet