By in situ simultaneous polymerization of dopamine and hydrolytic polycondensation of 3-aminopropyltriethoxysilane in an aqueous solution, a novel hybrid polymer network coating on stainless steel was formed. The polydopamine and silica hybrid polymer (PDSHP) adhered strongly on the surface of stainless steel. The PDSHP film provides active catechol and primary amine groups. Branched polyethylenimine was grafted based on the PDSHP film. The structure and morphology of the multilayer coating were characterized by attenuated total reflectance Fourier transform infrared spectroscopy reflectance, X-ray photoelectron spectroscopy, and atomic force microscopy and scanning electron microscopy images. The coatings on the stainless steel substrates exhibited anticorrosion of seawater. By making use of the primary amine groups on the multilayer coating, a biocidal agent 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) was grafted. The grafted CHPTAC was effective in killing bacteria, extending the multilayer polymer coating with biocidal functionality.