Prussian　blue　analogues　(PBAs)　are　recognized　as　promising　cathode　materials　for　sodium-ion　batteries　(SIBs)　due　to　their　facile　synthesis,　low-cost,　high　capacity,　and　environmental　friendliness.　However,　high　water　content　(＞10 wt%)　in　the　framework　and　unsatisfactory　structural　stability　of　PBAs　are　still　the　bottlenecks　for　industrial　applications.　Herein,　interstitial　K-doping　is　employed　to　minimize　the　interstitial　water　and　enhance　the　structural　stability　of　Na2-xFeMn[Fe(CN)6]　(FeMnPBA),　thereby　boosting　the　sodium　storage　performance.　The　3%　K-doping　(K-FeMnPBA3)　demonstrates　a　much-reduced　water　content　of　6.9%,　accompanied　by　a　notably　enhanced　capacity　of　139.1 mAh g−1　at　100 mA g−1　and　a　remarkable　capacity　retention　of　77.1%　after　700　cycles.　Furthermore,　the　K-FeMnPBA3/hard　carbon　(HC)　pouch　cell　achieves　a　stable　cyclability　with　82.6%　capacity　retention　after　600　cycles.　This　research　offers　valuable　insights　into　low-water　PBAs　for　practical　applications　in　SIBs.　©　2024　Wiley-VCH　GmbH.