The invention discloses a synthesis method of small core gold-coated ferric oxide core-shell structure nanoparticles, relating to the technical field of nanomaterials. The method comprises the following steps of: 1) adding an iron salt solution comprising ferrous chloride and ferric trichloride according to the volume ratio of 1: 10 into a NaOH solution, stirring, collecting produced black precipitates by a magnet, washing with water for three times to obtain fresh ferroferric oxide nanoparticles, dissolving in a nitric acid solution, heating and stirring till complete oxidation of gamma-Fe2O3, performing centrifugal collection after the solution is cooled, and washing with the water to obtain the ferric oxide nanoparticles of 3-6nm; and 2) diluting with the water till 1.1mM, adding sodium citrate, stirring, and alternately adding hydroxylamine hydrochloride and 1% of chloroauric acid for five times sequentially. The synthesis method has the beneficial effects that the method is simple to operate, the preparation conditions are mild, and the complex process of a conventional preparation method is avoided. Compared with single ferric oxide nanoparticles, the small core gold-coated ferric oxide core-shell structure nanoparticles have not only various properties of the ferric oxide nanoparticles, but also higher stability in comparison with the ferric oxide nanoparticles, and are widely applied to biological imaging, biosensing, biological identification and surface-enhanced Raman technologies.