In view of the complexity of the core structure of the brushless AC exciter and the influence of saturation characteristics of the ferromagnetic material, the finite element software Maxwell was used to create a twodimensional model of the brushless AC exciter for the research and analysis of noload characteristics and rated excitation current. Taking a 28 kW brushless AC exciter as an example, the simulation analysis of the air gap magnetic field of the motor and the calculation of the noload characteristics were carried out. The calculated fundamental wave potential was consistent with the measured results, and a theoretical basis for the design of the electromagnetic field of this type of motor was provided. Based on this, through fieldcircuit coupling method, the external circuit was used to simulate the rated load condition, and the excitation current under rated condition was calculated. This method had practicality and could provided reference for the calculation of the general AC exciter excitation current.