Abstract: In recent years, hydrovoltaic technology, which can output electricity by natural evaporation of water or adsorption of water vapor into materials, has attracted much attention of researchers. Featuring its low cost, controllable performance and no additional mechanical energy input, it is an enchanting energy conversion method with great development potential. In the past five years, the power density of hydrovoltaic devices has been greatly boosted, and the peak power of the pulse can reach mW/cm². As an alternative energy conversion technology based on the coupling between water and material surface to generate electric energy, hydrovoltaic effect not only enriches the energy conversion paths, but also provides the possibility to collect huge energy contained in water. This article summarizes hydrovoltaic device development in recent years based on different functional materials including carbon nanomaterials, semiconductor nanomaterials, organic nanomaterials, composite nanomaterials. In addition, we also discuss the device structure and electricity generation mechanism. Furthermore, their great potential in clean energy and portable flexible electronic equipment are outlooked.