The invention relates to a brushless exciter structure used for a three-level starting/power generating system and a control method of the exciter structure. The exciter structure is characterized in that a brushless exciter is of a rotating armature type structure, a stator exciting winding is of a two-phase symmetrically-distributed structure, and the two phases of the windings are spaced by a 90-degree electrical angle in space; a rotor armature winding is of a three-phase distributed structure, and the three phases of the windings are arranged at 120-degree intervals in electric angle in space. A double half-bridge two-phase inverter circuit or a double full-bridge two-phase inverter circuit or a three-phase full-bridge inverter circuit can be adopted as a two-phase inverter circuit. The exciter structure used for the three-level starting/power generating system and the control method of the exciter structure have the advantages that the exciter provides an enough exciting current for a main generator when a motor is motionless or runs at low speed or high speed, so that the main generator starts or generates power; compared with a single-phase winding method adopted for the exciting winding of the exciter, the method is high in alternating-current exciting efficiency and can meet requirements for the dual functions of starting and power generating of the large-power main generator.