Abstract: A rotating magnetic field detector with variable angle of the magnetic yoke was designed by converting the movement distance of the bottom joint of the rotating magnetic field detector into a change in the angle of the magnetic yoke, and the validation tests were conducted. Firstly, the magnetic field distribution and its variation pattern of the rotating magnetic field were obtained through theoretical calculation, and the trajectory and degree of magnetic field intensity variation were determined through simulation to confirm whether the theoretical calculation was correct. Then a sensitivity test block was manufactured to test the instrument's lifting force, effective magnetization range, and defect detection sensitivity, and determine the effectiveness of the current phase adjustment method. The experimental results showed that this method can achieve 100% detection of natural defects with a length of no less than 9 mm.