Unregulated interfacial electric fields critically undermine the stability of lithium-metal batteries (LMBs) by driving heterogeneous Li⁺ flux and dendritic deposition. Here, we report a dielectric-mediated electrolyte design that actively modulates the local electric field to enable uniform Li⁺ transport and Li⁰ deposition. By integrating fluorinated diluents with varying dielectric constants into localized high-concentration electrolytes (LHCE), a stable dielectric environment was constructed at the Li–electrolyte interface. Specifically, the high-dielectric diluent 1,1,1,3,3-pentafluorobutane facilitates electrolyte to realize uniform and flat lithium deposition under high current density of 3 mA·cm⁻² by suppressing the electrostatic tip effect that typically triggers dendrite formation. The optimized electrolyte achieves high Coulombic efficiency (> 99.5%), negligible growth in interfacial impedance, and stable cycling in thin Li-based cells. Moreover, Li (30 μm)||LiCoO₂ (3.6 mAh·cm⁻²) full cells retain 80% of their initial capacity after 250 cycles within a voltage window of 3–4.5 V, outperforming the reference cells (< 50 cycles) using high-concentration electrolyte and LHCE with low-dielectric-constant diluent. The strategy of dielectric-mediated interface homogenizes electric field distribution and stabilizes ion transport beyond conventional interphase-focused approaches. This work establishes dielectric modulation as a viable paradigm for interfacial regulation, advancing the design of high-energy-density LMBs.