Addressing the technical challenge of weak signals and low signal-to-noise ratio in eddy current testing of sub-millimeter ultra-fine tungsten wires, which hinders effective micro-defect identification, a novel eddy current testing method based on the energy dissipation principle is proposed. This method innovatively employs energy dissipation as a direct defect characterization parameter, leading to the design of an eddy current detection system centered on micro-power measurement. Numerical simulations based on established impedance and energy dissipation models of the core-type coil reveal that within the 0.1~1.0 mm wire diameter range, the energy dissipation signal decays more gradually with decreasing diameter and remains effective below 0.2 mm, outperforming traditional impedance method. A micro-power measurement system was consequently developed to acquire voltage, current, and phase difference in real time, enabling the calculation of active power to characterize energy dissipation caused by defects. Experimental investigations on diameter fluctuations and crack defects demonstrate that for a 0.05 mm diameter variation, the energy dissipation method yields a signal change of 4.59%, substantially exceeding the 0.11% and 0.21% achieved by traditional impedance and phase detection methods, respectively. For micro-cracks with depths of 0.05, 0.08, and 0.10 mm, the signal variation rates are 0.8%, 0.9%, and 1.1%, respectively, with standard deviations across five repeated measurements all below 0.08 mW, indicating exceptional repeatability, sensitivity, and measurement stability. Furthermore, continuous online testing of 0.40 mm tungsten wires on a production line successfully identified multiple micro-defects with varying locations and magnitudes, confirming the method′s feasibility and effectiveness in real industrial environments. Experimental results show that the proposed energy dissipation method significantly surpasses the traditional impedance approach in sensitivity, stability, and anti-interference capability, offering a new pathway for non-destructive testing of sub-millimeter tungsten wires and other ultra-fine filaments.