Abstract: Endogenous substances, such as organic acids in food, can interfere with the detection of trace residues. To eliminate this effect, the magnetic adsorbent material was obtained by directly modifying acidified Fe₃O₄ with N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane (KH792) as an amination reagent. The optimal modification condition of KH792 for acidified Fe₃O₄ was optimized by response surface methodology, which was 82.5℃, pH=4.9, and KH792 addition of 1.8 mL. Under these optimal conditions, the acidified Fe₃O₄ directly modified by KH792 has an adsorption capacity of 22.8 mg/g and shows a 188% increase in the adsorption capacity of the gallic acid compared to commercially available Fe₃O₄. Additionally, the modified Fe₃O₄ exhibits excellent performances of rapid solid-liquid separation, good stability, and dispersibility. The properties of the directly modified products were characterized by BET, Zeta potential, FTIR, and XPS. The results show that KH792 bonds on Fe₃O₄ surface hydroxyl group's by Fe—O—Si bonding, and acidification improves the number of hydroxyl groups on Fe₃O₄ surface, thus improving the KH792 modification for Fe₃O₄. The magnetic products prepared in this work can be used for the purification of organic acids in complex sample matrices.