To realize the accurate measurement of mT magnitude magnetic gradient tensor in small space for traveling wave main magnetic flux leakage of high-speed maglev track stator, the Prewitt gradient operator of image edge detection is instantiated. A small volume and low-cost Hall magnetic gradient tensor measurement structure including 8 Hall magnetic sensors is designed. It overcomes the characteristics of large zero drift and poor sensitivity consistency of the Hall magnetic sensor by spatial redundancy, which provides a new way for sensors spatial layout design of the magnetic gradient tensor system. Compared with the traditional cross and square structure, experimental results show that the Prewitt structure can reduce the measurement error caused by the inconsistency of the above two parameters of multi-sensors to - 10. 4% and 58. 1% . The requirements of the measurement system for the consistency of sensor parameters is effectively reduced, and the complex and high-cost calibration of the three-axis sensor and error correction are avoided.