Sc and Zn were introduced into O3-NaMn_0.5Ni_0.5O₂ (NaMN) using the combination of solution combustion and solid-state method. The effect of Sc and Zn dual-substitution on Na⁺ diffusion dynamics and structural stability of NaMN was investigated. The physicochemical characterizations suggest that the introduction of Sc and Zn broaden Na⁺ diffusion channels and weaken the Na—O bonds, thereby facilitating the diffusion of sodium ions. Simulations indicate that the Sc and Zn dual-substitution decreases the diffusion barrier of Na-ions and improves the conductivity of the material. The dual-substituted NaMn_0.5Ni_0.4Sc_0.04Zn_0.04O₂ (NaMNSZ44) cathode delivers impressive cycle stability with capacity retention of 71.2 % after 200 cycles at 1C and 54.8% after 400 cycles at 5C. Additionally, the full cell paired with hard carbon anode exhibits a remarkable long-term cycling stability, showing capacity retention of 64.1% after 250 cycles at 1C. These results demonstrate that Sc and Zn dual-substitution is an effective strategy to improve the Na⁺ diffusion dynamics and structural stability of NaMN.