Na3V2(PO4)2O2F (NVPFO) attracts tremendous attention as a cathode material for sodium-ion batteries (SIBs) because of its higher capacity and structural stability. However, its inherent poor conductivity affects rate performance and long cycle performance. Herein, a special lamellar NVPFO are successfully synthesized by sodium alginate (SA) assisted hydrothermal method. SA dissolves in water to form hydrogel, due to the specific cross-linking of SA and V4+, which restricts the crystal growth of nanoparticles. Meanwhile, a conductive carbon layer for sodium ion transport channels is constructed after carbonization. Based on multidimensional experiments and density functional theory (DFT) calculations, a mechanism for formation of special lamellar NVPFO in SA solution is proposed for the first time. The results show that special lamellar morphology shortens Na+ migration path and conductive coating facilitates electronic transmission. The optimized NVPFO@C-2 has better electrochemical performance with outstanding high rate capacity (106.8 mAh g–1 at 15 C) and long-term cyclability (99.8 mAh g−1 capacity retention of 87.1 % even after 1000 cycles at 5 C).