The invention discloses a three-phase brushless synchronous generator with compound excitation, which comprises a stator assembly and a rotor assembly. The rotor assembly comprises a generator field iron core, a generator field winding on the generator field iron core, an exciter iron core and an exciter winding on the exciter iron core, wherein the generator field iron core and the exciter iron core are arranged on the same rotor shaft in parallel; and the stator assembly comprises a generator iron core, a generator main winding on the generator iron core, an exciter field iron core and an exciter voltage field winding on the exciter field iron core. A three-phase output line of the generator main winding is provided with a Y-connection three-phase current mutual inductor, the stator assembly is provided with a current compound excitation winding for exciting the exciter winding, and the output end of the three-phase current mutual inductor and the current compound excitation winding form a closed loop by a three-phase bridge rectifier circuit. The invention greatly improves the capability of a generator for starting an asynchronous motor, solves the problem of great transiently output voltage change of the generator with an abruptly added or discharged rated load and improves the transient performance index of the output voltage of the generator.