The invention discloses a method and a control device for recycling potential energy of a movable arm of an excavator. When the movable arm descends, first-stage pressure boosting can be realized in a controlled manner according to difference between the area of a rodless cavity of an oil cylinder of the movable arm and the area of a rod cavity of the oil cylinder of the movable arm, then second-stage pressure boosting is realized via a pressure boosting cylinder, the potential energy generated during descending of the movable arm can be converted into high-pressure energy through the two stages of pressure boosting, and the high-pressure energy is stored in an energy accumulator; and when the energy is released, high-pressure oil stored in the energy accumulator is led into an oil inlet of a rotation control valve in a controlled manner, pressure oil in the energy accumulator is led into a rotation motor through the rotation control valve, and rotation operation can be carried out. By the method and the control device for recycling the potential energy of the movable arm of the excavator, the energy can be reused, designing, manufacturing and overall arrangement of the pressure boosting cylinder are facilitated, and the energy of the energy accumulator can be released and used.