The invention relates to an energy-saving hydraulic system for a crane. The energy-saving hydraulic system solves the problems that an existing energy-saving hydraulic system for the crane is large in energy loss, large in system heating amount and poor in control performance. The energy-saving hydraulic system comprises an oil tank, an amplitude variation oil cylinder, a main roll motor, an auxiliary roll motor, a stretchable oil cylinder, a first pump motor, a first one-way valve, a second pump motor and a second one-way valve; the first pump motor is connected with the oil tank through the first one-way valve, and the second pump motor is connected with the oil tank through the second one-way valve; the first pump motor is connected with the amplitude variation oil cylinder and the main roll motor through a first switching valve, and the second pump motor is connected with the amplitude variation oil cylinder and the auxiliary roll motor through a second switching valve; and the first pump motor and the second pump motor are both connected with the stretchable oil cylinder through a third switching valve. By means of the energy-saving hydraulic system, smooth switching of all actions is achieved, and the effect of composite actions is improved; and the energy-saving hydraulic system has the beneficial effects of being stable in control, saving energy, recovering energy relatively easily, few in hydraulic element and the like.