Natural water evaporation (NWE) is spontaneous and ubiquitous process that absorbs ambient thermal energy. Scavenging ambient thermal energy into electricity by NWE provides a promising approach to supply power for self-powered and low-cost devices and systems. Suitable materials and techniques are required to use this ubiquitous natural process for electricity generation. Herein, a continuous NWE-driven flexible generator is fabricated by painting Ni-Al layered double hydroxide (LDH) on a polyethylene terephthalate substrate at room temperature. The generator operates through an NWE-driven gradient of water that flows across the naturally formed surface-charged nanochannels between Ni-Al LDH flakes; i.e., the streaming potential mechanism. The output electrical characteristics of the device can be controlled by adjusting the environmental moisture and wind velocity. Continuous electricity output with a comparatively high power density of 16.1 μW cm−3 is achieved from a generator. The generator can maintain a stable output power under deformation. The output power of the generator can be scaled up to continuously power integrated circuit devices such as a digital calculator. Given the easy fabrication process of this flexible NWE-driven generator using an environmentally friendly LDH and its continuous electricity output with relatively high power density, this generator represents an important step towards practical green ambient energy harvesting.