Electromagnetic field (EMF) treatment has demonstrated its superior efficiency and great potential in inhibiting scale formation in industrial plants. Despite the numerous studies focusing on improving the performance of EMF devices, there is still limited understanding of how the frequency affects the anti-scaling process. This problem restricts the development and optimization of the sweep frequency EMF technique, which is assumed to have a better anti-scale performance. In this work, experimental studies were performed to study the effect of the sweep frequency EMF on the precipitation of CaCO₃ under circulating flow conditions. The results showed that the sweep frequency EMF could stimulate the homogeneous crystallization of CaCO₃ in the simulated hard water solution, and the direct reaction between Ca²⁺ and HCO₃^- was the primary reaction route. The sweep frequency had a more pronounced effect on the scale formation process than the output current of the EMF device. The sweep frequency value was inversely correlated with the scale formation. The effect mechanism of sweep frequency on the scale formation process was discussed.