Hard carbon is a promising anode material for sodium-ion batteries due to its low cost and high capacity. However, its practical application has been largely hindered by poor rate performance and long-term cycling degradation resulting from the continuous consumption of electrolyte and growth of a solid electrolyte interface (SEI). Here, we propose a facile oxygen plasma treatment strategy to modify the surface of hard carbon to stabilize the SEI. By this method, the specific capacity has been considerably enhanced from 225 mA h g-1 (for the pristine hard carbon sample) to 325 mA h g-1 at a current rate of 50 mA g-1. Furthermore, the modified sample demonstrated long-term cycling stability and remarkable rate performance. The performance enhancement was attributed to the stabilization of the solid electrolyte interface through interaction between the electrolyte and the surface oxygen functional group, reducing the continuous consumption of electrolyte and formation of a stable solid electrolyte interface. This surface treating strategy is simple, scalable, and easy to extend to modify diversified battery materials.