Abstract: In order to solve the indefects that magnetic nano-Fe₃O₄ particles were corroded and agglomerated easily, functional modification was carried out. FeCl₃ and FeSO₄ were used as raw materials and ammonia as preci-pitant in the presence of ultrasonic irradiation, then functionalized by ethyl orthosilicate (TEOS) and 3-aminopropyltrimethoxysilane (APTMS) to prepare SiO₂-coated amino-functional nanocomposites Fe₃O₄@SiO₂-APTMS. The magnetic nanocomposites were characterized by TEM, FTIR, VSM, TGA, low temperature nitrogen adsorption and XRD, etc. The characterized results show that the magnetic nanocomposites prepared by ultrasonic strengthening method have the characteristics of strong magnetic response, strong acid and alkali resistance, high dispersion, large specific surface area and small particle size.Meanwhile, the adsorption effects of magnetic nanocomposites for Pb(Ⅱ) were investigated. The results show that the initial pH value of the solution and the dosage of adsorbent have greatest effects on the adsorption effect of Pb(Ⅱ) with the initial pH value of the solution 5.86 and the dosage of adsorbent 1.0-1.5 g·L⁻¹. The Langmuir model is suitable for simulating the isothermal adsorption process, and the adsorption process is a spontaneous process when Gibbs free energy change ∆G⁰<0. The adsorption behavior of Pb(Ⅱ) can be well described by quasi-second-order kinetics on the composites, Quasi-second-order kinetic constant k₂=0.0401 g·mg⁻¹·min⁻¹, equilibrium adsorption capacity q_e=80.041 mg·g⁻¹; it is speculated that the adsorption mechanism is mainly complex adsorption and ion exchange.