The invention discloses an energy regeneration system of a combined hydraulic cylinder. The energy regeneration system comprises a hydraulic valve controller, a weight M, a first plunger hydraulic cylinder, a single-piston-rod hydraulic cylinder, a second plunger hydraulic cylinder, a hydraulic cylinder fixing frame, a first one-way valve, a second one-way valve, a speed regulation valve, a thirdone-way valve, a fourth one-way valve, a fifth one-way valve, a two-position two-way reversing valve, a hydraulic energy accumulator, a two-position three-way reversing valve, a three-position four-way reversing valve, an oil tank and a variable hydraulic pump. During the falling process of the weight M, high-pressure oil passes through the fourth one-way valve and enters the hydraulic energy accumulator through an A-C oil way of the two-position three-way reversing valve, and the gravitational potential energy of the weight M is stored in the hydraulic energy accumulator. In the process of lifting the weight M, hydraulic energy stored by the hydraulic energy accumulator can pass through a C-B oil path of the two-position three-way reversing valve and is provided to a rodless cavity of thesingle-piston-rod hydraulic cylinder through the fifth one-way valve and the second one-way valve to lift the weight M so as to achieve the purpose of energy regeneration.