Ferric chloride modified lotus stem-based porous carbon (FeCl3-LSPC) was synthesized for the removal of bromate from aqueous solutions. The adsorbent characterization indicated that the BET surface area and pore volume were enlarged by the modification of FeCl3, at the same time, the reductive functional group of C-OH was enhanced in the FeCl3-LSPC. The FeCl3-LSPC exhibited greater bromate removal performance in a wide pH range compared to other absorbents. The mechanisms of bromate removal were analyzed by XPS and two-dimensional correlation analysis of FTIR (2D-FTIR-COS). The main removal mechanism of bromate is reduction and C-OH group was responsible for bromate reduction. During the bromate reduction process, the Fe3+/Fe2+ redox couple served as electron shuttle to facilitate the electron transfer from C-OH group to bromate. The main functional groups involved in bromate reduction process followed the reaction order: C-OH > C=O > COOH > C-H.