The invention relates to a defect detection method based on fast and slow wave chasing, and the method comprises the following steps: 1, calculating a guided
wave frequency dispersion curve of a one-dimensional component, and determining the propagation speeds of guided
waves under different frequencies, 2, selecting two excitation frequencies, respectively corresponding to different propagation speeds, recording a fast wave with a fast propagation speed as a fast wave, recording a
wave speed as V1, recording a slow wave with a slow propagation speed as a slow wave, 3, when the fast
waves reach the meeting point, if the point has defects, the defects are fully expanded under the stretching action of the slow
waves, so that the reflection of the fast waves is improved, 4, the excitation time interval of the fast waves and the slow waves is
delta t, and 5, the emission time interval is continuously changed, so that the fast waves and the slow waves meet at different positions d, and the reflection of the fast waves and the slow waves is improved. And step 6, extracting the intensity of the fast wave echo signals at different d positions as a (x), obtaining a corresponding relation curve of the
echo intensity and the length of the component, and if the curve is obviously increased at a certain position, determining that the position has defects.