[Objective] This paper addresses the cogging torque inherent in fractional-slot concentrated winding (FSCW) stator axial-flux dual-rotor synchronous generator, which can induce vibration and acoustic noise, degrade control accuracy and operational smoothness. The virtual displacement method is employed to analyze the underlying mechanism of cogging torque generation and to derive its approximate analytical expression, thereby providing a theoretical basis for generator design, manufacturing, and optimization. [Methods] First, the fundamental theory of FSCW was reviewed, and the structural characteristics and coupling principle of an electrically excited through-FSCW-stator axial-flux dual-rotor synchronous generator (AF-DR-TS-FSCW-SG) were introduced. Subsequently, the cogging torque generation mechanism of this class of generators was analyzed using the virtual displacement method, and an analytical expression for cogging torque was derived based on the magnetomotive force-permeance method, yielding an approximate mathematical model. In addition, a two-dimensional finite element modeling approach tailored for axial-flux dual-rotor synchronous machines was proposed, and its accuracy was validated through no-load electromagnetic characteristic experiments. Finally, the dominant subharmonic amplitudes of cogging torque obtained from the analytical model were compared with those derived from two-dimensional finite element simulations. [Results] The results indicated that the relative errors of the no-load back electromotive force (EMF) amplitude between the two-dimensional finite element analysis (2-D FEA) results and the experimental measurements under three operating conditions—namely, excitation of rotor 1 alone, excitation of rotor 2 alone, and simultaneous excitation of both rotors—were 4.02%, 16.84%, and 10.73%, respectively. Despite the amplitude discrepancies, the waveform variation trends showed good agreement among all cases. Meanwhile, for the operating conditions with rotor 1 alone and rotor 2 alone excited, the relative errors of the dominant harmonic component of the cogging torque between the 2-D FEA results and the analytical results obtained by the virtual displacement method were 13.86% and 13.57%, respectively. [Conclusion] The proposed two-dimensional finite element modeling approach for the FSCW-stator axial-flux dual-rotor synchronous generator in this paper can accurately reflect the actual performance of the generator. In addition, the cogging torque mathematical model derived based on the virtual displacement method exhibits high accuracy.