<p>Due to their open framework and high theoretical capacity, Prussian blue analogues (PBAs) have emerged as promising cathode materials for sodium-ion batteries. Nevertheless, their electrochemical performance is often compromised by defects in the structure, like coordinated water and Fe(CN)₆ vacancies, which are influenced by synthesis conditions. Here, we design a molecular weight gradient of PAAs (4 kDa, 8 kDa, 150 kDa, 3–7 MDa, and 30–50 MDa) and its effect on regulating the structure-performance relationship of Prussian blue cathode materials. Characterization results reveal that higher-molecular-weight sodium polyacrylate (30–50 MDa) as a chelating agent can effectively minimize Fe(CN)₆ vacancies and reduce lattice water content (10.5 wt%) by increasing crystalline stability through the steric effects as dominant and coordination as an adjunct. Consequently, the optimized PB cathode delivers a superior reversible 147 mAh g⁻¹ capacity at 0.2 C and outstanding cycling stability (82.6% retention after 50 cycles). Kinetic analyses demonstrate improved Na⁺ diffusion kinetics and reduced charge-transfer resistance in the high molecular weight PAAs-derived PB, attributed to its more robust crystalline framework. This study clarified the optimizing effect of molecular weight differences on the performance of Prussian blue when polymers are used as chelating agents, providing a feasible strategy for the development of high-performance PB-based cathodes.</p>