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Abstract Surface strain engineering is a promising strategy to design various electrocatalysts for sustainable energy storage and conversion. However, achieving the multifunctional activity of the catalyst via the adjustment of strain engineering remains a major challenge. Herein, an excellent trifunctional electrocatalyst (Ru/RuO2@NCS) is prepared by anchoring lattice mismatch strained core/shell Ru/RuO2 nanocrystals on nitrogen‐doped carbon nanosheets. Core/shell Ru/RuO2 nanocrystals with ~5 atomic layers of RuO2 shells eliminate the ligand effect and produce ~2% of the surface compressive strain, which can boost the trifunctional activity (oxygen evolution reaction [OER], oxygen reduction reaction [ORR], and hydrogen evolution reaction [HER]) of the catalyst. When equipped in rechargeable Zn‐air batteries, the Ru/RuO2@NCS endows them with high power (137.1 mW cm−2) and energy (714.9 Wh kgZn−1) density and excellent cycle stability. Moreover, the as‐fabricated Zn‐air batteries can drive a water splitting electrolyzer assembled with Ru/RuO2@NCS and achieve a current density of 10 mA cm−2 only requires a low potential ~1.51 V. Density functional theory calculations reveal that the compressive strained RuO2 could reduce the reaction barrier and improve the binding of rate‐determining intermediates (*OH, *O, *OOH, and *H), leading to the enhanced catalytic activity and stability. This work can provide a novel avenue for the rational design of multifunctional catalysts in future clean energy fields.