The key to the development of sodium ion battery is materials with a high rate capacity and cycle stability. Conducting coating is an efficient approach to improve electrochemical performance. As a case study, the Na3V2(PO4)3@PEDOT composite was prepared through an in-situ self-decorated conducting polymer route without further calcination. The Na3V2(PO4)3 electrode with a 7% poly(3,4-ethylenedioxythiophene) (PEDOT) coating can deliver an initial reversible capacity of 100 mA h g−1 at 1 cycle, and 82% capacity retention over 200 cycles. The results also show that the Na3V2(PO4)3 electrode without and with a thick PEDOT coating exhibits poor electrochemical performance, indicating that an appropriate coating layer is important for improving electronic conductivity and regulating Na-ion insertion. Therefore, this work offers possibility to promote the electrochemical performance of poor-conducting materials in sodium-ion batteries using an in-situ self-decorated conducting polymer.