Abstract: The current transformer (CT) on-line energy acquisition devices are difficult to acquire energy under small currents, and the magnetic core is saturated under high currents. To solve such problems, a stable energy acquisition method based on adaptive impedance adjustment was presented. Through parallel resonance, a double branch model including damping branch and energy taking branch was constructed to realize current transfer and solve the problem of energy harvesting with low bus current. An impedance adjustment method based on quality factor adjustment was proposed to stabilize the load power in a certain current range. An impedance adjustment method based on reverse current injection was put forward to solve the core saturation problem when the bus current is large. Aiming at the sudden change of bus current, an impedance adjustment method based on bypass resistance switching was proposed to realize fast impedance adjustment and avoid energy impact. The simulation and experimental systems were established. The experimental results show that the method can not only achieve high power output, but also stabilize the load power in a wide range current, which can meet the energy demand of on-line monitoring equipment of transmission lines.