Abstract: The Xiluodu-Zhexi800 kV UHV DC transmission line passes through the Xiangxi area where the traffic is very inconvenient, the ground is undulating and the geological conditions are complex. Engineering drilling work carried out in this region is very difficult. Preliminary exploration data show that at the limestone area, karst development is strongly. Tower pad stability can face safety threats. At the sandstone district, the covering clay layer contains weathered debris. Ordinary twist drill is difficult to accurately determine the coverage layer thickness. In order to check the karst development situation and the bedrock surface depth, the ground penetrating radar was used to detect the strata after the pre-test demonstration. In addition to the ground penetrating radar detection on the ground, we also carried out the pile bottom detection in order to further investigate the karst development less than 5m under the bottom of the hole. Drilling and excavation results show that the ground penetrating radar can effectively detect the hidden karst, bedrock surface, weathered zone, fracture and fracture zone. It provides a scientific basis for reasonable choice tower bit and design foundation depth. It achieves a good application result.