Surface enhanced Raman spectroscopy (SERS) is a technique widely used in detecting analytes at low concentrations and could provide structural information at the sametime. It is necessary to find the optimal particle size, shape and spatial distribution to optimize the SERS substrate. Current research efforts are focused on fabricating new kind of nanocomposite using as SERS substrates. Porous materials have long been employed as SERS substrate because of their unique features, the porosity that enable them as efficient adsorbents for target molecule. The porous α⁃Fe2O3 was used as solid support. In this paper, porous nano α⁃Fe2O3 was synthesized by hydrothermal method using porous α⁃Fe2O3 as solid carrier, and then calcined into Fe, so that there were porous channels on the surface of Fe. PATP aqueous solution and melamine aqueous solution were used as probe molecules. By adjusting the size of Au nanoparticles and investigating its influence on SERS performance, the optimum performance of 50 nm Au was obtained.The structures and compositions of the nanocomposites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X⁃ray diffraction (XRD), and N2 adsorption. Our research illustrates a new kind of porous Fe2O3⁃Ag nanocomposite, that could be used as effective SERS substrate to adsorb and detect trace level of target analyte.