[Objective] This paper aims to address the issue of high content of non-dominant harmonics and significant torque pulsation in fractional slot concentrated winding (FSCW) dual-rotor synchronous motors. A compensation winding is proposed to optimize the magnetic field structure of dual-pole-pair coupling, suppress non-dominant pole-order harmonics, and increase the content of dominant harmonics, thereby reducing torque pulsation caused by non-uniform magnetic fields. [Methods] Firstly, the fundamental theory of FSCW was analyzed, and the structural characteristics and coupling principles of dual-rotor synchronous motors were introduced. The algebraic and phasor synthesis methods were employed to analyze the distribution patterns of harmonic magnetomotive force in FSCW under different slot-pole combinations, and the distribution coefficients were derived. Subsequently, based on the distribution of dominant and high-content non-dominant pole-order harmonics, as well as the peak and valley characteristics of the synthesized magnetomotive force, a direct compensation method for specific harmonics was designed. The virtual displacement method was used to derive the expression for electromagnetic torque. Finally, finite element simulation and theoretical calculations using the virtual displacement method were conducted to analyze the changes in air-gap flux density and torque pulsation before and after harmonic compensation. [Results] The finite element simulation results showed high consistency with the theoretical calculations using the virtual displacement method, verifying the accuracy of the method for torque calculation. The electromagnetic torque waveform exhibited better sinusoidal characteristics after adding the compensation winding, and the torque pulsation of both rotors was significantly reduced. Specifically, after adding 1-pole compensation windings, the torque pulsation of Rotor 1 and Rotor 2 decreased by 30.11% and 41.1%, respectively. [Conclusion] The proposed method can effectively suppress the high-content non-dominant harmonics, optimize the torque waveform, and reduce the torque pulsation, thereby enhancing the operational efficiency of the motor.