Abstract: The principle of magnetic flux leakage detection is stated.The principle is verified by 2D electromagnetic field simulation based on ANSYS system.Further more,the 3D finite element method is used to analyse leakage magnetic field and 3D model of magnetic flux leakage detection is also established.The distribution regularity of magnetic induction with no defect specimen and the distribution regularity of 3D leakage magnetic field with defective specimens are obtained based on the ANSYS solutions.Meanwhile,the influences of defect geometric parameters both on the total magnetic induction intensity and on the axial component are studied.And the influence of current intensity on the total magnetic induction intensity is also obtained.According to the results of ANSYS analysis,it is easy to find that there exists a non-detection zone by magnetic flux leakage detection.Finally,by adding a guide specimen to the original specimen,the problem of the non-detection zone in the end of specimen is solved and the feasibility of the total testing is verified by simulation.