Abstract: The flux-gate magnetometer is used to measure the parallel component of the magnetic field of the deep-lying eddy current, which can avoid the influence of the exciting coil when the central magnetic field of the exciting coil is perpendicular to the measurement direction. This method could distinguish line defect and cross defect clearly, and the detection depth of multi-layer Al plates was as high as 14 mm. It was found that the amplitude of the eddy current magnetic field signal of cross defect was greater than line defect, and it decreased slower when the depth of the defect was increasing.