Abstract: Magnetic flux leakage(MFL) testing method usually measures the two components of MFL of being perpendicular and parallel to the surface defect of MFL to quantitatively detect the defects. However, it is very difficult to quantitatively detect the complex surface defects in rail track by the traditional method. In order to overcome the disadvantage of this method, the three-dimensional (3D) magnetic field measurement method and finite element analysis(FEA) were used to analyze the distribution of MFL. A 3D detecting system for rail surface defect was designed to test samples with several artificial defects samples. The results showed that perpendicular component contained important defect information, especially for the defects non-vertical to the rail track.