Abstract: To solve the problems of current transformer (CT) inductive energy harvesting mode in transmission lines, such as difficulty in obtaining maximum power at low current, easy saturation of magnetic core at high current and unstable energy harvesting caused by current fluctuation of transmission line, this paper proposes an online energy harvesting method based on equivalent impedance matching of voltage source rectifier (VSR) was proposed. First, a VSR energy harvesting equivalent circuit model is constructed, and the relationship between the parameters of the circuit model and the output power of CT is deduced. Then, considering the characteristic of CT as a current source (the port voltage amplitude is determined by the transmission line current, excitation parameters and load characteristics), a control strategy of constant d-axis current, constant DC voltage outer loop and q-axis current inner loop is proposed. The amplitude and phase of VSR port voltage and current are controlled in real time, VSR is equivalent to the adjustable impedance to dynamically match with CT excitation impedance, and then the CT port voltage is indirectly controlled to a fixed value. With the aim of verifying the effectiveness of the method in this paper, simulation and experimental systems are built. The results show that the equivalent impedance of VSR is capacitive when the transmission line current is low, which can achieve the maximum power output of CT at low current of the transmission line, and the equivalent impedance of VSR is inductive when the transmission line current is high, which can inhibit the saturation of CT magnetic core. It can meet the power supply requirements of some low-power devices on transmission lines.