Triclinic Na2−x Fe1+x/2P2O7/C composite was prepared by glass-ceramics method. We found that Na2−x Fe1+x/2P2O7/C composite can be used as cathode active materials for Sodium ion battery with high current density rate performance over 10C (2 mA cm−2) condition and stable electrochemical cycle performance. A 2 μm glass precursor powder in composition of Na2−x Fe1+x/2P2O7 (x = 0–0.44) was crystallized in tubular furnace around 600 °C with carbon source to reduce iron valence state and to coat grain surface with carbon. By means of charge–discharge testing Na2FeP2O7/C composite exhibits 86 mAh g−1 (253 Wh kg−1) as reversible discharge energy density that is half amount of that for LiFePO4, however in 10C condition they kept 45 mAh g−1 (110 Wh kg−1) even in 2 μm grain size.