Abstract: To address the issue of low efficiency in finite element simulation of three-dimensional transformer magnetic field, a magnetic field reduction model based on intrinsic orthogonal decomposition method and a loss response surface model based on quadratic polynomial were proposed. A 110 kV transformer was taken as an example, the transformer magnetic field simulation model considering winding eddy current losses was first established, and its magnetic field and loss distribution under rated operating condition were analyzed through simulations. Secondly, the magnetic field and loss data under various operating conditions were obtained through designed-test simulations, and the reduced order modules of transformer magnetic field were obtained through training in Twin Builder. Finally, a three-dimensional magnetic field reduction model for transformers available to digital twin applications was constructed, achieving a rapid calculation of transformer magnetic field losses and visualization of cloud map distribution. Compared with the calculation sheet data, the simulation results show that the winding loss considering eddy current effect will significantly increase near the winding ends, with their maximum values appearing at both ends of the high and low voltage windings, approximately 1.3~1.65 times the loss in the middle of the winding. The reduced order model which is established based on the magnetic field results will reduce the actual simulation time to 0.76 seconds, which can meet the rapid calculation requirements of magnetic fields in digital twin application scenarios and demonstrates its superiority over the full order model.