NOVELTY - A power generation system and a method using hydraulic pressure are provided to obtain electric energy by operating horizontally a cylinder by the difference of hydraulic pressure and to use effectively natural energy with the low cost.    DETAILED DESCRIPTION - In a power generation system and a method using hydraulic pressure, cylinders of first and second hydraulic cans(k1,k2) are combined integrally with a cylinder(13) by a connecting bar(14). The cylinder is installed in the first and second hydraulic cans. First and second hydraulic pressure cut-off plates(s1,s2) are assembled to the first and second hydraulic cans. A valve(21) and a hydraulic pressure control pipe(20) are attached on the first and second hydraulic pressure cut-off plates and mounted under the water. The hydraulic pressure of the first hydraulic can cylinder is high by the pressure of the external water by opening the first hydraulic pressure cut-off plate. The hydraulic pressure of the second hydraulic can cylinder is low by closing the second hydraulic pressure cut-off plate. Power of the first hydraulic can cylinder with the high hydraulic pressure moves the second hydraulic can cylinder to produce electric energy. When the cylinder reaches the end of the right side of the second hydraulic can and the first hydraulic pressure cut-off plate is closed, the hydraulic pressure is lowered and the cylinder stops temporally. The hydraulic pressure of the second hydraulic can cylinder is increased by the pressure of the external water by opening the second hydraulic pressure cut-off plate. The first hydraulic can cylinder is lowered by closing the first hydraulic pressure cut-off plate. The power of the second hydraulic can cylinder with increased hydraulic pressure moves the first hydraulic can cylinder with lowered hydraulic pressure and produces the electric energy. When the cylinder reaches the left end of the first hydraulic can and the second hydraulic pressure cut-off plate is closed, the hydraulic pressure is lowered and the cylinder stops temporally.