Materials and technologies which can resist the adhesion of microorganisms, purify the wastewater and transport fluid with lower drag have been explored avidly, but a number of challenges still remain. A hydrogel coating anchored on the structured surface was fabricated through a facile surface self-catalyzed polymerization in situ. The necessary physicochemical properties of as-prepared hydrogel substrate were characterized, and the experimental results indicated that a controllable fluid drag was achieved through regulating the weak interaction between the mobile oil phase and hydrogel surface, meanwhile, the corresponding maximum of drag reduction efficiency was up to 64%. Besides, driven solely by gravity, the porous hydrogel-based iron net prototype was capable of generating purified seawater at a high rate of permeation flux 42,000 L m−2 h-1, and its longer-time application for either oil/water separation or fluid transportation could be preserved with the help of high efficiency antifouling behavior and good abrasion resistance capability. As a consequence, because of the remarkable drag reduction behavior and high-efficiency oil/sea water separation ability, hydrogel coated but structured substrate fabricated using a facile, cost-effective, and scalable method is expected to open up new avenues for large-scale sea water purification, oil transportation application and some other relevant fields.