The emerging moist-electric generation that can harvest energy from the atmosphere moisture to power the next-generation wearable electronics has attracted great attention recently. However, currently developed moist-electric generators (MEGs) are hard to be fully stretchable owing to the lack of essential material properties and the restriction of the device construction. Here, stretchable hygroscopic ionic hydrogel and carbon black-coated cotton knitted fabric are employed with a pair of symmetric Cu electrodes on top and bottom to fabricate a fully stretchable moist-electric generator (FSMEG). The prepared FSMEG simultaneously achieves outstanding stretchability of 400%, sustained short-circuit current of 50 µA, and open-circuit voltage of 0.3 V, demonstrating superior comprehensive performances among current MEGs. The remarkable performances of FSMEG can be ascribed to the decreased crystallinity of ionic hydrogel and the synergistic effect of water evaporation force and redox reaction on electrodes. Of great importance is that large-scale integration of FSMEG units is capable of driving electronics including calculators, light-emitting-diodes, and even cell phones. Beyond power generation, FSMEG also successfully exhibits practical application in self-powered pressure sensing and weight identification. The optimal properties and design concepts of FSMEG provide new insight for designing next-generation high-performance hydroelectric harvesting devices with wide applications.