NASICON (Na-super-ionic-conductors)-structured materials have attracted extensive research interest due to their great application potential in secondary batteries. However, the mechanism of capacity fading for NASICON-structured electrode materials has been rarely studied. In this paper, we synthesized the NASICON-structured Na3V2(PO4)3/C composite by simple sol–gel and high-temperature solid-phase method and investigated its electrochemical performance in Na–Zn hybrid aqueous rechargeable batteries. After characterizing the structure, morphology and composition variations as well as the interfacial resistance changes of Na3V2(PO4)3/C cathode during cycling, we propose a mechanical and interfacial degradation mechanism for capacity fading of NASICON-structured Na3V2(PO4)3/C in Na–Zn hybrid aqueous rechargeable batteries. This work will shed light on enhancing the mechanical and interfacial stability of NASICON-structured Na3V2(PO4)3/C in Na–Zn hybrid aqueous rechargeable batteries.