Current transformers are fundamental to the control and protection of distribution networks, and their measurement accuracy under wide-frequency conditions directly impacts the safety and stability of the power grid. This study conducts wide-frequency modeling and analysis of the commonly used electromagnetic current transformers in low-voltage distribution networks, deriving their error transfer functions. The effects of frequency, ranging from 20 to 3000 Hz, on the measurement errors—namely, ratio error and phase error—are analyzed, and the findings are validated through Matlab simulations. The conclusions provide valuable references for the application of electromagnetic current transformers under wide-frequency conditions.