Abstract: As the voltage increases, the volume of large power transformer enlarges continuously. So people have to disintegrate the transformer core for transportation. However, the change of structure may cause leakage field distribution of maldistribution and local overheating. The 3D electromagnetic field in power transformer simulation of three-phase five-column transformer short-circuit performance and the calculation of the leakage magnetic field is based finite element method. The difference between simulation results and the experimental results is rather small which verifies the accuracy of the simulation.