The work aim to detect and protect the iron nails used in the Palace Museum buildings. Metallographic analysis of the iron nail matrix was performed with a metallographic microscope, and the surface of the rust layer was observed by a stereomicroscope. Scanning electron microscopy, X-ray spectroscopy (SEM-EDX), and X-ray diffraction (XRD) were used to test the chemical composition of the corrosion products. The kinetic potential polarization curve was measured to study the electrochemical behavior of silicate compound corrosion inhibitors on the pre-film corrosion inhibition of cast iron electrodes. Polyethylene glycol (PEG) was added to modify the silicate compound corrosion inhibitors. The structure of the iron nails matrix used for the Palace Museum buildings was nodular cast iron. The surface corrosion products were mainly reddish brown and dark brown. After analysis, the corrosion products were mainly composed of Fe2O3, Fe3O4 and α-FeOOH. The main component of the white substance on the surface of the nails was CaCO3. The corrosion inhibition efficiency measured by the polarization curve method was 20.53% after pre-filming with silicate compounded inhibitor, and the corrosion inhibition efficiency reached 81.20% after modification. AC impedance test, salt spray resistance test and outdoor exposure test all showed that the modified corrosion inhibitor had certain corrosion inhibition performance. The surface of the iron nails used in the Palace Museum buildings was heavily rusted, and a series of protection measures are needed to slow the corrosion rate. The effect of silicate compound inhibitor after pre-filming is not good. The modified inhibitor has certain corrosion inhibition effect on the cast iron sample simulating iron nails, and the surface color changes slightly, which meets the protection requirements of iron cultural relics.