Abstract: To reduce the volume of magnetic flux leakage detector and enhance flexibility of inline inspections, the finite element analysis method is used under non-magnetic saturation conditions to construct the finite element model for detection of magnetic flux leakage and then determine impacts of weak magentic excitation to detection of magnetic flux leakage. In addition, detection accuracy, characteristics and distribution laws of weak magnetic signals are analyzed. The results show that the weak magentic technology can be used for detection, but with accuracy reduced by about 40%. For pipeline defects with depths at 30%-40% of wall thickness, radial weak magentic signals of external defects are undistinguishable. For defects with widths less than 2 mm, amplitudes of axial components of weak magnetic signals of external defects are lower than those of internal defects. The simulation results may serve as criteria for determination of internal or external defects. In addition, these results may provide valuable guidance to improve structure of detectors.