sodium ion batteries are considered as excellent energy storage battery materials with the characteristic of low cost and renewability. As a critical component of sodium-ion energy storage batteries, cathode materials have attracted great attention from scientists around the world. Recently, Na4Fe3(PO4)2P2O7 (NFPP) which offer a theoretical capacity of 129 mAh g-1 has garnered widespread attention. However, the formation of inactive maricite NaFePO4 (NFP) and low capacity Na2FeP2O7 (Na2FPO) during the synthesis process restricts the capacity utilization, while poor conductivity further limits its electrochemical performance. To address these issues, here, Na3.95Fe2.95V0.05(PO4)2P2O7/C (V0.05-NFPP/C) composite material was synthesized and assembled into cell for testing. A capacity of 114 mAh g-1 was given at 0.1C and rate performance also represent 90 mAh g-1 at 10C. Vanadium-ion improves the dynamic performance by inhibiting maricite NFP and participating in electrochemical reactions. Furthermore, sodium-ion storage mechanism of V0.05-NFPP/C was revealed by ex-situ XRD patterns with the assistance of first-principles calculations, and the phase transformation mechanism during the sintering process was explored.