To improve antifouling and anticorrosion properties of stainless steel (SS), well-controlled polycationic brushes were robustly anchored on the steel substrates by biomimetic polydopamine layers. Self-polymerization of dopamine on the steel surface was first carried out to introduce an alkyl bromine atom transfer radical polymerization (ATRP) initiator. Subsequent grafting of the cross linked poly(2-(dimethyamino)ethyl methacrylate (PDMAEMA) layer from the bromine-terminated steel substrates was accomplished by surface-initiated ATRP of DMAEMA with poly(ethylene glycol) dimethacrylate (PEGDMA) as a cross linker, followed by N-alkylated reaction of the PDMAEMA chains to introduce a high surface density of positively charged quaternary ammonium salts. The as-synthesized SS substrates tethered with cross-linked polycationic brushes demonstrated enhanced antifouling against the Amphora coffeaeformis attachment and barnacle cyprids settlement and exhibited good antibacterial and anticorrosion effects against the marine bacteria Pseudomonas sp. The functionalized SS substrates with good antifouling and anticorrosion capabilities are potentially useful in marine environments.