This article develops a kind of core-shell structure with optical magnetic properties and conjugates it with fluorescent labels to synthesize nanocomposite particles. For the pure Fe3O4 nanoferrofluid prepared by chemical co-precipitation method, its average particle size is 25 nm, and a layer of zinc sulfide shell is absorbed on the surface of Fe3O4 nanoparticles. Inspection by xi-potentialmeter shows that the surface of Fe3O4 particles carries positive charge, thus increasing the efficiency of its conjugation with oligonucleotide. The prepared Fe3O4/ZnS core-shell nanocomposite particles are conjugated with two groups of oligonucleotide and a bridge oligonucleotide primer with different sequences, and then they are mixed. These three groups of oligonucleotide primer base with different sequences are designed to be partially complementary and are mutually conjugated together through the hybridization of DNAs. As supported by colormetric reporter gene, the hybridization technology for different sequences of DNA developed by this article is proved successful.