In this paper, , the combination of antenna array detection method of ground penetrating radar is put forward to solve the actual engineering problem that is difficult to monitor the integrity of the flexural pile composite foundation. The experiments of defects of six tamping soil cement piles find that the relative error of the pile position of defects is 5.25%. The result indicates that it is enough reliability to determine the pile defects by using the GPR method and can meet the engineering needs. Furthermore, the effect of age of cement, the ration between soil and cement, depth and types of defects on the monitoring quality is obtained.