Cattail-grass-derived porous carbon as high-capacity anode materials were prepared via high-temperature carbonization and activation with KOH. The samples exhibited different structures and morphologies with increasing treatment time. It was found that the cattail grass with activation treatment—1 (CGA-1) sample obtained at 800 °C for 1 h presented excellent electrochemical performance. As an anode material for lithium-ion batteries, CGA-1 showed a high charge–discharge capacity of 814.7 mAh g−1 at the current density of 0.1 A g−1 after 400 cycles, which suggests that it has a great potential for energy storage.