Cadmium(Cd)contamination poses significant risks to agricultural productivity and ecosystems, necessitating effective remediation strategies. This study evaluated the efficacy of iron (Fe)-modified corn straw biochar (FB) in immobilizing Cd and reducing its uptake in lettuce, compared to raw biochar (B). FB was synthesized by pyrolyzing Fe(NO₃)₃-treated corn straw and characterized for physicochemical properties. Pot experiments tested Cd immobilization at 0, 1, and 2 mg kg⁻¹ Cd levels with 0%, 1%, and 3% (w/w) B or FB applications. Results demonstrated that FB exhibited higher specific surface area, pore volume, and oxygen-containing functional groups than B, enhancing Cd adsorption via mechanisms including surface complexation (-OH, Fe-O), precipitation (CdCO₃), and π-π interactions. FB reduced soil bioavailable Cd by 15–28% and shifted Cd speciation from exchangeable to Fe/Mn oxide-bound fractions, outperforming B even at lower doses (1% FB ≈ 3% B). Additionally, FB improved soil fertility, enzyme activities, and enriched Cd-immobilizing bacteria , promoting lettuce growth and reducing Cd content in roots (25–40%) and leaves (33–47%). The findings highlight FB as a cost-effective and sustainable amendment for Cd-contaminated soils, combining enhanced adsorption, microbial modulation, and reduced application rates. This study provides critical insights into Fe-modified biochar’s dual role in soil remediation and crop safety, supporting its practical application in sustainable agriculture.