Abstract: As one kind of underground works, many factors of cut-off walls like human causes and material/technique differences may lead to construction defects. In order to detect the location and distribution of the defects and identify whether the wall bottom has been embedded into the foundation rock, high-density seismic imaging method and transient Rayleigh wave method are used considering the in-situ geological information and construction technique. The inversion software GeoCOD and GeoRwa are combined to make analytical interpretation and the results are cross-checked with core-drilling results, confirming that this seismic survey approach is applicable to cut-off walls detection. In view of the heavy labor involved in cut-off wall quality testing, the practice proves that the seismic survey technology can thoroughly locate the possible distribution range of the defects in an effective, fast, non-destructive and economical way, which can provide technical support for risk elimination and reinforcement of embankment.