Abstract: To address the limitations of insufficient active sites and low adsorption capacity of pristine biochar for ammonia nitrogen (NH₄⁺), a phosphate-intercalated magnesium-iron layered double hydroxide/biochar composite (MgFe-LDH/BC-P) was prepared via coprecipitation using corn straw biochar as the substrate, and the preparation conditions were optimized using response surface method (RSM). Key factors including pyrolysis temperature, Mg/Fe molar ratio, and KH₂PO₄ dosage were screened through single-factor experiments, and a predictive model for NH₄⁺ adsorption capacity was established using Box-Behnken design, which determined that the optimal preparation conditions are a pyrolysis temperature of 372.81℃, a Mg/Fe molar ratio of 3.97, and a KH₂PO₄ dosage of 1.13 g. Under these conditions, the composite material exhibited an NH₄⁺ adsorption capacity of 38.36 mg/g, which showed a high degree of consistency with the model prediction. Characterization results from BET, SEM, FTIR, XPS, and Zeta potential analyses indicated that after successfully loading of MgFe-LDH onto the biochar surface and inserting of PO₄³⁻ into the LDH interlayer, a stable mesoporous structure was formed, and the negative charge on the material surface was enhanced. Adsorption kinetics and isotherm studies showed that the adsorption process followed the pseudo-second-order kinetic model and the Langmuir isotherm model, with a theoretical maximum adsorption capacity of 53.51 mg/g, suggesting monolayer chemical adsorption as the dominant mechanism. The composite exhibits controllable preparation and excellent adsorption performance, providing a promising approach for efficient NH₄⁺ removal from water.