Exploiting new carbon supports with adjustable metal-support interaction and low price is of prime importance to realize the maximum active iron efficiency and industrial-scale application of Fe-based catalysts for Fischer-Tropsch synthesis (FTS). Herein, a simple, tunable, and scalable biochar support derived from the sugarcane bagasse was successfully prepared and was first used for FTS. The metal-support interaction was precisely controlled by functional groups of biosugarcane-based carbon material and different iron species sizes. All catalysts synthesized displayed high activities, and the iron-time-yield of Fe/C even reached 1,198.9 μmol g s. This performance was due to the unique structure and characteristics of the biosugarcane-based carbon support, which possessed abundant C-O, C=O (η(O) and η(C, O)) functional groups, thus endowing the moderate metal-support interaction, high dispersion of active iron species, more active ε-FeC phase, and, most importantly, a high proportion of FeC/Fe, facilitating the maximum iron efficiency and intrinsic activity of the catalyst.