Abstract: The setting depth of bagged sand well is a technical index to be controlled in the treatment of soft foundations by the drainage consolidation method. It is of great significance to develop an effective method for in-situ testing the depth of bagged sand wells to ensure the treatment effects of the drainage consolidation method. The results show that the average consolidation degree of soft soil foundation is approximately linearly positive correlated with the depth of bagged sand well. The artificial magnetic field set in the sand bag as the detection mark of the end of the bagged sand well has significant recognition. The detection target preset at the bottom of the sand bag has a good success rate when the sand bag is set to a predetermined depth. By controlling the magnetic field strength of the magnetic core in the target and the distance between the two cores, the influences of the natural magnetic field and adjacent targets can be avoided. It has good maneuverability and accuracy to detect the spatial position of the target synchronously with the penetration magnetic sensors in the static penetration mechanical system. The field tests show that the magnetic field method can meet the engineering needs and has a significant cost performance advantage compared with the high pressure water flushing method.