As a high-efficiency, non-destructive geophysical method, ground penetrating radar (GPR) has been widely applied to detection of subsurface pipes in urban areas. The detection and localization of water pipe leakage is of great significance. In this paper, a controlled model experiment was carried out to investigate of the characteristics of GPR signal reflected from the leakage area surrounding a water pipe buried in sand. Oscillation signal trailing the reflection from the top of the pipe in radar image is found after the water leakage. The phenomenon is further interpreted by conducting a full wave simulation of electromagnetic waves propagation though the leakage area. The results are important to accurately interpret field GPR data to localize water leakage.