Abstract: In order to achieve the ultrasonic detection of surface micro-cracks, a geometric model of surface acoustic waves with nonlinear responses containing surface micro-cracks was constructed based on COMSOL. The effect of the selection of surface wave mixing frequency on modulation was analyzed, and the influence of different crack lengths, widths, and propagation distances on the sideband components were studied. A surface micro-crack detection method was proposed based on the second harmonic and sideband components. The results show that the second harmonic component can be used to determine the presence of micro-cracks, and the normalized sideband component can locate and quantitatively analyze those micro-cracks. A negative correlation is observed between the sum of crack length and sideband component, while a linear negative correlation is observed between propagation distance and the sum of sideband component, with a correlation coefficient of 0.963 for the linear fitting curve.