The detection of concrete interface position is the key to control the overfilling height of the pile. The traditional method of determining the concrete interface position by manual experience has a large error and cannot effectively control the filling height. It is difficult to discriminate the concrete interface during pouring, which leads to the problem of underfilling or overfilling of concrete. The first method of overfilling detection based on magnetic detection technology is proposed. Firstly, the magnetic target is designed by using the density difference of different media in the borehole, and then by measuring and processing the three-component data of magnetic field, the concrete interface position is detected to control the concrete filling height. This paper designs a set of overfill detection system based on magnetic detection technology, completes the selection of measurement points through indoor tests, and designs the magnetic target specific gravity as 2.1 g/cm3, and the alarm threshold is calibrated as 333 mG. Through construction site tests, it is verified that the system achieves rapid detection of concrete interface to the pile elevation and overfill ceiling position, and accurately completes two levels of warning to achieve automatic detection, which solves the problem of It solves the problem of concrete underfilling or overfilling at the construction site, and effectively reduces the waste of concrete.