Manganese‐based layered oxides are currently of significant interest as cathode materials for sodium‐ion batteries due to their low toxicity and high specific capacity. However, the practical applications are impeded by sluggish intrinsic Na+ migration and poor structure stability as a result of Jahn–Teller distortion and complicated phase transition. In this study, a high‐entropy strategy is proposed to enhance the high‐voltage capacity and cycling stability. The designed P2‐Na0.67Mn0.6Cu0.08Ni0.09Fe0.18Ti0.05O2 achieves a deeply desodiation and delivers charging capacity of 158.1 mAh g−1 corresponding to 0.61 Na with a high initial Coulombic efficiency of 98.2 %. The charge compensation is attributed to the cationic and anionic redox reactions conjunctively. Moreover, the crystal structure is effectively stabilized, leading to a slight variation of lattice parameters. This research carries implications for the expedited development of low‐cost, high‐energy‐density cathode materials for sodium‐ion batteries. A high‐entropy strategy is applied to design a new P2 phase cathode material for sodium‐ion batteries, aiming to improve stability in deeply desodiated states. This material exhibits superior reversibility with 0.61 Na extracted, attributed to triggered lattice‐oxygen redox reaction activity and facilitated Na+ migration. As a result, it demonstrates excellent initial Coulombic efficiency, high energy density, and lengthened cycling performance.