The current transformer (CT) is an effective harvester for high-voltage transmission lines. However, when the traditional CT supplies power to the online monitoring equipment, the large-scale fluctuation of the transmission line current will not only lead to insufficient power supply of the CT (when the current is low), but also saturate the iron core of the CT (when the current is high). In view of the above problems, this paper proposes a method for realizing the high-power harvester based on the impedance converter. According to the level of the transmission line current, control the impedance converter to work in different modes to realize the dynamic adjustment of the output impedance from capacitive to inductive, and ensure that the CT maintains stable output voltage and power when the current of the transmission line changes in a large range. At the same time, the equivalent modeling of the CT is carried out through simulation and experiment, which verifies the effectiveness of the scheme proposed in this paper. The CT power density at 60 A is 9.91 W/kg.