A carbon-coated K_0.76V_0.55Nb_0.45OPO₄ (KVNP@C) polyanion material was successfully synthe- sized by a simple sol-gel method. The KVNP@C possesses a highly stable inorganic open-framework structure, which is hard to be affected by the Na⁺ intercalation/deintercalation when used as an anode material for sodium-ion batteries (NIBs). The assembled KVNP@C/Na half-cell shows a capacity retention of 81.2% and an average Coulombic efficiency of 99.8% at a current density of 300 mA/g after 1500 cycles. In-situ XRD analysis reveals a single-phase solid solution reaction mechanism with a lattice expansion of 4.76%. This work sheds insights into the quest for developing novel polyanion-based anode materials for sodium-ion batteries.