To address the problem of micro-cracks detection on the surface of cold-rolled rolls, this article proposes an alternating current magnetic flux leakage detection method excited by double-layer flexible parallel cables, which is used to profile the working surface of the rolls, and uses the high-precision tunnel magnetoresistance ( TMR) sensor array as the detection sensor. It has the ability to detect micro-cracks on large curvature surfaces. Meanwhile, by adjusting the excitation current of the double-layer PCs to offset the tangential component of the background magnetic field, the excitation current is increased further and the TMR overrange saturation problem is avoided. The tangential component of the magnetic field is used to characterize defects, enabling it to characterize multidirectional cracks in a single scanning direction. Based on the analysis above, this article establishes a three-dimensional finite element simulation model of double-layer PCs and roll, and studies the influence of roll radius, defect angles and depth on AC MFL signal through simulation. Finally, a corresponding verification experimental platform is established. Experiment shows that the probe can effectively magnetize the surface with large curvature, detect and distinguish multidirectional cracks, and detect micro-cracks at a depth of 15 μm.