By analyzing various power supply sources for on-line monitoring device along transmission line, a newly current transformer(CT) energy-absorbing source combined super capacitor and lithium battery was put forward to amend the drawbacks of the existing one for our research group, namely inefficiency, core saturation, output voltage instability and existing dead zone. High-capacity super capacitor with ideal filtering effect and anti-saturation performance were put just after the rectifying circuit. Moreover, the relation between capacitor’ voltage and core’s power-absorbing efficiency was analyzed to obtain the proper value of capacitor voltage that is helpful for CT to remain the highest efficiency absorbing energy from transmission line. In addition, CT can work very well in different conditions along with different line currents through managing circuit and lithium battery. The test data verified that the newly developed CT energy-absorbing power source had advantages such as high efficiency, non-saturation state of CT, stable operation, eliminated dead zone of power supply and large instantaneous output power.