Stray loss of large single-phase power transformer tank influenced its efficiency and reliability. Magnetic material was usually attached on the inner wall of the transformer tank in order to reduce the stray loss. However, the magnetic field surrounding the ferromagnetic shielding was enhanced and resulted in local overheat of the tank. Various structures of ferro- and/or non-magnetic thin-layers are proposed and modeled by 2D and 3D finite element analysis (FEA) in this paper. Simulation results showed that the stray losses could be effectively reduced by using non-magnetically metallic layer between ferromagnetic layer and tank wall with optimal shielding thickness.