Potassium-ion　batteries　(KIBs)　are　a　promising　alternative　to　Lithium-based　energy　storage　systems　owning　to　the　low　cost　and　rich　abundance　of　potassium　resources,　but　are　facing　challenges　in　designing　low-cost　hosts　that　can　reversibly　accommodate　large-size　1(4　with　fast　diffusion　kinetics.　Herein,　we　report　a　novel　3D　inorganic　open　framework　of　Ca2Nb2O7　(CNO)　as　an　anode　for　KIBs.　The　open　framework　structure　affords　interstitial　vacancies　available　for　storing　K+　and　allows　a　facile　diffusion　of　K+,　thus　resulting　in　excellent　structural　stability　and　fast　reaction　kinetics.　The　CNO　electrode　delivers　a　reversible　specific　capacity　of　65.3　and　52.2　mAhig　at　5　and　10　mAig,　respectively.　Moreover,　CNO　exhibits　excellent　long-term　cyclability　with　92.53%　capacity　retention　over　700　cycles　at　10　mAig.　This　will　trigger　more　investigations　into　open-framework-based　materials　for　stable　and　fast　KIBs.