The current transformer (CT) harvester is an effective and efficient solution due to its higher reliability and power density compared to other techniques. However, the current of overhead conductor fluctuates from tens of to thousands of amperes, which brings two challenges for the CT harvester design. First, the startup current, above which the harvester can independently power the monitoring devices, should be as low as possible, so that the battery capacity can be reduced; secondly, the magnetic core should be ensured unsaturated in high current condition. This paper proposes a power conditioning circuit with comprehensive control to maximize the output power and prevent the core from saturation. A prototype that can deliver 22.5 W power with 200 A is designed, and a control strategy based on the finite-state machine is implemented. Experimental results show that the startup current for 2 W load is about 30 A, and the core power density at 60 A is 45.96 mW/cm3, both of which are markedly improved compared to the reported results of the same condition.