As a common hydraulic structure, sluice foundation poses a hidden danger that seriously affects its quality and safety. After the sluice has been operated for a period of time, it tends to form a hollowed out area as the water flow erodes the foundation soil at the bottom of the sluice. In the long run, piping has been caused, which poses a serious threat to the safety of the sluice and the lives of the people. Therefore, this paper aims to provide guidance for the grouting treatment scheme by taking a sluice with piping along the Qiantang River as an example. To achieve this objective, the whole area is detected by ground penetrating radar, the void or non dense position is delineated, and the specific depth and range of the void area are verified by borehole television. Following grouting treatment, the original position is retested by radar, and the radar images are compared before and after grouting in the void area to analyze and evaluate the outcome of grouting treatment. The test results indicate the obvious response of the GPR to the void position. By verifying drill hole TV, more intuitive image evidences are gathered for the void position, and the specific depth of void is measured. Moreover, the radar images are compared before and after grouting to qualitatively evaluate the outcome of grouting treatment.