Power device based on alkali-water reaction, having a reaction chamber to carry out a chemical reaction between water and alkali element, having an exhaust nozzle to exhaust the reaction products generated in the reaction chamber, with a siphon tube connected to the exhaust nozzle, a nozzle shutter plate sealing the exhaust nozzle, and an external pressure inlet. The device has a water reservoir to store transfer water to the reaction chamber and an alkali reservoir to store and transfer an alkali element to the reaction chamber, and transfer device connecting the reaction chamber to both reservoirs to transmit the pressure generated in reaction chamber by part of the reaction products to the reservoirs, providing the transfer of water and alkali element from both reservoirs to the reaction chamber.