Fluxgate-based direct current transformer (DCCT) is widely used in applications such as instrument calibration and current monitoring in DC power distribution, where extremely high precision is required. To meet the demand, the ripple in the output signal must be minimized, with induced modulation ripple being the dominant component of the output ripple. Therefore, it is essential to model and analyze the transmission characteristics of the induced modulation ripple and investigate corresponding suppression methods. Based on the typical structure of fluxgate-based DCCT, a transmission model for induced modulation ripple was proposed. The coupling and propagation mechanisms of the ripple were analyzed, and a transmission function was derived according to the magnetic characteristics of the system. Key factors affecting the suppression of induced modulation ripple were identified, providing a theoretical basis for the design of parameters in closed-loop feedback structures. The results show that, with the model′s guidance, the output ripple at the fundamental frequency of the prototype is attenuated by 53.4 dB, consistent with the theoretical predictions.