Nano-wrinkled polymeric membranes have received tremendous attention for their broad applications in tunable optics, biomedicine, surface wettability, and flexible electronics. However, achieveing a low-cost and scalable synthesis routine remains highly desirable. Here, we invent a simple, bottom-up, polymer engineering strategy by introducing water molecules into the polymerization process. Water evaporation induces intermolecular forces that build a crosslinking reaction gradient from the material surface to its interior, which buckles the surface-forming wrinkles. The shape, geometry, size, orientation, and arrangement of the wrinkles on the polymer surface can be designed accordingly. Moreover, the as-fabricated nano-wrinkled, polymeric membranes display outstanding performance in energy and sensing applications, boosting output current and sensing sensitivity by 611% and 164%, respectively, compared to their flat counterparts. This work may contribute to a low-cost, scalable, and environmentally friendly strategy to engineer polymer surfaces with controllable wrinkles, showing great potential for the development of various soft-matter technologies.