Abstract: Regarding the stray loss problem of three-phase auto transformer with large capacity, a simplified three-dimensional transformer model is established. The ANSYS FEM software is utilized to calculate the leakage magnetic field and loss density distribution in clamps and tank wall without magnetic shield are calculated. The effects of two types of clamp magnetic shields and two different arrangements of magnetic tank shields on the leakage magnetic field and loss density are analyzed. Finally, the simulated values of stray loss are obtained under two different combination options. By comparing the experiment values, option 2 reduces stray losses by 112.6 kW to option 1. The experimental and simulated values are very close to each other and the error is very small. It indicates that the established model and simulation method demonstrate a high level of accuracy and reliability. Meanwhile, the experimental values also show that the stray loss in transformer can be significantly reduced by using a combination of lobe type magnetic shield and vertical tank magnetic shield. This study not only advances the theoretical understanding of stray loss in transformer, but also provides valuable guidance for engineering practices, highlighting its application and practical significance.