In this work, we experimentally synthesized the Fe<sub>3</sub>O<sub>4</sub>@Au nanocomposites and used them as surface-enhanced Raman scattering (SERS) substrates. The Fe<sub>3</sub>O<sub>4</sub>@Au nanocomposites retained the metallic plasmon resonant effect and possessed the magnetic field controllable characteristics. The Raman spectra of Rhodamine B (RhB) probe molecules were studied under different external magnetic field. The magnitude of external magnetic field varied from 0 Gs to 700 Gs (1 Gs = 10<sup>−4</sup> T) with intervals of 100 Gs. When the magnetic field magnitude increased, the Raman intensity of RhB probe molecules at 1356 cm<sup>-1</sup> increased linearly. The slope of the linear fitting curves for the Raman intensity and area were 0.118/Gs and 3.700/Gs. The Raman enhancement could raise up to 7 times for RhB probe molecules when the magnetic field magnitude increased to 700 Gs. After removing the external magnetic field, the Raman peaks returned to its original intensity in several minutes. Under the external magnetic field, the Fe<sub>3</sub>O<sub>4</sub>@Au nanocomposites were concentrated, leading to the increase number of SERS “hot spots” and the surface Au density. The results show that the magnetic field controlled Fe<sub>3</sub>O<sub>4</sub>@Au nanocomposites can realize the enhanced and controllable SERS effect, which can be used in the reversible optical sensing and bio-medical applications.