Based on the grid data collection, this paper proposes a 3D slice imaging algorithm for rebar concrete component detection by structure scan radar. First, Kirchhoff migration is used to focus so that the reflection wave is returned to its real space position automatically. Then 3D interpolation is carried out to obtain the enough space information of targets for reconstructing with only a few measured data. At last, two direction profiles are fused together to enhance targets response, reduce noise influence, and improve detection efficiency. The detection of experiment platform and true architecture validate the availability and feasibility of the algorithm. The results indicate that exact inner information of rebar concrete component is known comprehensively and meticulously via 3D slice imaging of structure scan radar data. The algorithm can separate dot targets as well as horizontal and vertical linearity targets clearly and supply a credible method and basis for the explanation of radar profile, thus having great significance for relevant detection project and quality identification.