Although hard carbon is deemed to be the most potential industrialized sodium-ion batteries anode material, there are still some problems need to be solved. In this study, a waste biomass of reed straw is pretreated by using a new strategy-hydrothermal treatment instead of pickling and successfully transformed to hard carbon materials through subsequent carbonization process. The reed straw carbonized at 1300 °C exhibits an impressively high reversible capacity of 372.0 mAh g−1 with excellent initial coulombic efficiency of 77.03% and outstanding cycling stability. Significantly, the sodium storage mechanism in our electrodes is mainly summarized into two models. Moreover, we find the interlayer spacing of graphite-like nanocrystal of obtained hard carbon influences the sodium ion diffusion ability, thereby affecting the rate performance. Our work offers a simple and eco-friendly way for converting biomass to highly capacity carbon as well as a towardly anode material for sodium-ion batteries, which will open up new avenues of other biomass carbon materials with promising applications.