Abstract: To address the critical issue of lubricating film rupture induced by Joule heating under current-carrying conditions, this paper introduces polar carbon-based nanocomposites （PCN） featuring high Zeta potentials. An anti-thermal degradation strategy is proposed, which utilizes the electric field to actively modulate the rheological properties of the fluid. Based on the Asymmetric Electric Double Layer （AEDL） theory, a numerical model for point contact elastohydrodynamic lubrication （EHL） is established. This model incorporates a competitive mechanism between thermal thinning and electro-viscous enhancement. Simulation results indicate that the electro-viscous effect generated by PCN fluids under contact voltage induction effectively compensates for thermally induced viscosity loss. Consequently, the critical frequency required to enter the full-film lubrication regime is reduced by approximately 50%. Ball-on-disc current-carrying tribological experiments confirm that under low-frequency, heavy-load, and current shock conditions, the base oil undergoes severe boundary lubrication failure. In contrast, the PCN fluid maintains a low and stable friction coefficient. This study reveals the physical nature of the “electric-thermal” competition and provides a theoretical basis for the lubrication design of current-carrying transmission systems.