The invention discloses a method and system for generating power by using nuclear fusion. According to the method and system of the invention, energy generated miniature nuclear fusion which works under a non-critical state is utilized to lift the level of water; the gravitational potential energy of the water is utilized to generate power; a fusion target and laser ignition are adopted to realize nuclear fusion; laser is inputted into an end portion of the glass tube of the fusion target; a laser shock ignition technique is utilized to make a deuterium pellet experience fusion; the explosion equivalent of the deuterium pellet each time is safe for a nuclear reaction well; under a condition that the reaction well is not damaged, the level of the water in the nuclear reaction well is lifted through each miniature nuclear explosion, so that the water will flow into an external annular reservoir; a power generation device is arranged at the bottom of the annular reservoir; and the difference of the elevations of the bottom of the annular reservoir and the sea level is utilized to generate power. The system provided by the invention is an unlimited, clean and safe new energy power generation system using nuclear fusion.