Tests and verifications were conducted under various working conditions to confirm the effect of ground penetrating radar (GPR) in detecting shield tunnels. This provided a practical basis for GPR in detecting the backfilling quality of a shield tunnel. The research shows that the dense steel structure of the shield segment can shield the electromagnetic wave and cause multiple oscillations. The structural differences of different measuring line positions also increase the difficulty of detection. GPR can detect interface anomalies on the backs of shield tunnel segments by carefully selecting the antenna and optimizing the acquisition process. Choosing a single shield segment as the minimum determination unit to qualitatively determine the grouting density behind the segments is reasonable. The corresponding relationship between the intensity of the radar image anomalies and the size of the defects needs to be verified in the future.