Conventional sliding mode triboelectric nanogenerators convert low-frequency mechanical energy into electricity through relative motion between solid-solid tribo-layers. However, the inherent trade-off between maintaining close contact and mitigating interfacial friction hinders the device's energy conversion efficiency and long-term stability. Here, a solid-like liquid-slider triboelectric nanogenerator (LS-TENG) is proposed, where milliliter-scale liquid motion is precisely governed by a liquid-driver consisting of a hydrophilic interface enclosed by a hydrophobic boundary. By theoretical analysis and experimental regulation of solid–liquid–gas three-phase interfacial forces, stable operation of the liquid-slider with a designed pattern is realized as the tilt angle varies from horizontal to vertical. Benefiting from the shape-adaptivity and ultra-smooth properties of the liquid, a palm-sized LS-TENG outputs 2856 µJ of energy per cycle with an average torque of just 0.73 mN·m at 30 rpm, achieving a record-high energy conversion efficiency of 63.47%. The optimized friction during solid-liquid dynamic interactions ensures the excellent stability of LS-TENG over six months of continuous operation. Moreover, the encapsulated LS-TENG autonomously initiates under a 1.3 m s−1 breeze, powering 960 series-connected green LEDs and enabling wireless wind speed monitoring. The regulation of three-phase interfacial forces in solid-liquid TENG provides a feasible path for efficient and reliable mechanical energy harvesting.