The sodium orthosilicates as the potential candidates of cathode materials in sodium-ion batteries capture tremendous interests because of the low costs, robustly crystal structure and high specific capacity. However, like lithium orthosilicates, the crystal structure, morphology and electrochemical properties of the polycrystalline sodium orthosilicates need to be properly designed so that sodium ion can be smoothly intercalated/deintercalated. Herein, a novel orthorhombic Pb21 a–Na2FeSiO4/C, which is obtained from the conversion of C2221–Na2FeSiO4/C, is prepared and used as cathode material for the first time. Meanwhile, the pure phase C2221–Na2FeSiO4/C is firstly prepared by sol-gel method. Field emission scanning and transmission electron microscopy demonstrate that C2221–Na2FeSiO4/C has quasi-spherical morphology, and the active nanoparticles completely disperse within the cross-linked carbon nanolayer. The results from X-ray diffraction and Rietveld analysis reveal that the crystal structure of Pb21 a–Na2FeSiO4/C, similarly to C2221–Na2FeSiO4/C, can be formed by three-dimensional channel networks which generate from the alternate tetrahedral geometry chains of [FeO4] and [SiO4], but Pb21 a–Na2FeSiO4/C composite is more stable than C2221–Na2FeSiO4/C. After the first sodiation/desodiation process, Pb21 a–Na2FeSiO4/C shows the specific capacity of 118 mAh g−1 at 0.1 C and a capacity retention of 57.3% after 100 cycles.