In order to investigate the quenching effect of magnetic graphene oxide(Fe3O4/GO) on fluorescence, Fe3O4/GO was prepared using chemical method and then characterized using scanning electron microscopy(SEM), transmission electron microscopy(TEM), X-ray diffraction(XRD) and Fourier transform infrared spectroscopy(FT–IR). The results showed that Fe3O4 magnetic nanoparticles successfully synthesized and were loaded on the surface of GO. In its application on quenching, the Fe3O4/GO was used as the fluorescence quenching agent, and the fluorescence probe of salmonella was used as the fluorescence agent. The fluorescence quenching mechanism of Fe3O4/GO was preliminarily analyzed by fluorescence and ultraviolet absorption spectra, combined with Stern-Volmer equation and Lineweaver-Burk double reciprocal curve equation. The results showed that Fe3O4/GO had fluorescence quenching effect. When the concentration of Fe3O4/GO was 3.2×10?4 g/mL, the fluorescence quenching rate was up to 96.86%, in a static quenching way. Moreover, Fe3O4/GO fluorescence probe complex has good selectivity in the detection of salmonella DNA.