Sodium　ion　batteries　(SIBs),　an　immensely　attractive　substitute　to　lithium-ion　batteries,　have　received　significant　attention　in　applications　of　large-scale　energy　storage　and　transportation　owing　to　the　abundant　reserves　of　sodium　and　highly　sufficient　similarity　to　lithium.　Among　carbon-based　materials,　hard　carbon　(HC)　is　expected　to　be　a　promising　host　for　sodium　ions,　offering　high　thermodynamic　stability　when　charge　transfer.　However,　the　limited　understanding　of　HC＇s　structural　characteristics　and　sodium　binding　mechanism　presents　a　significant　challenge　to　the　rational　design　of　high-performance　HC.　Here,　by　employing　an　independently　developed　Neural　Network　Potential　(NNP)　model　for　NaC　binary　system　with　certain　experimental　techniques,　fundamental　HC　structure　and　the　correspondence　between　each　segment　of　voltage　curve　and　sodium　storage　sites　are　reproduced.　Additionally,　intrinsic　atomic　scale　structure-property　relationship　underlying　high　capacity　in　HC　is　uncovered.　It　is　highlighting　that　the　competition　between　the　Na-Na/Na-C　interaction　ratio　is　identified　as　a　critical　factor　determining　the　attribute　of　voltage　curve,　leading　to　the　discovery　of　a　novel　＇adsorption-insertion/filling＇　hybrid　(de)sodiation　mechanism.　These　findings　advance　methodologies　for　analyzing　amorphous　materials　and　providing　atomic-level　insights　to　guide　more　precise　structural　optimization　for　HC,　facilitating　the　development　of　superior　electrode　materials　for　next-generation　sodium-ion　batteries.　©　2025　Elsevier　B.V.