The magnetic Fe₃O₄ nanoparticles were prepared by a co-precipitation method. The magnetic nanoparticles (MNPs) with core-shell structure were constructed by alkali-catalyzed hydrolysis of tetraethyl orthosilicate, and SnCl₂ grafted on MNPs (SnCl₂@MNPs) was successfully synthesized by a co-precipitation method. Then the catalyst of SnCl₂@MNPs was further analyzed by a series of modern characterization methods for exploring the microstructure and composition. The results showed that SnCl₂ was uniformly dispersed on the surfaces of MNPs and there were strong interaction forces between SnCl₂ and MNPs. Subsequently, the Biginelli reaction was performed to investigate the catalyst performance, the results showed that 3,4-dihydropyrimidin-2(1H)-ones were efficiently synthesized by a three component one-pot reactions of aromatic aldehydes or heterocyclic aldehydes, carbamide or thiourea, andα,β-dicarbonyl compounds with high yields of 78%~96%. The active fraction of SnCl₂ in SnCl₂@MNPs is uniformly distributed on the surface of MNPs and in the form of microcrystalline that increases the effective contact area with substrates. The highly activity of SnCl₂@MNPs is ascribed to the synergistic effect of SnCl₂ and the abundant hydroxyl cluster in MNPs. In addition, the catalyst can be recovered using an external magnetic field and reused at least 7 times without a considerable decrease in its catalytic activity.