Aiming at the problem of large energy waste in large excavator slewing hydraulic systems,taking CED1000-7 excavator as the research object, in the study of the traditional open-type hydraulic slewing system energy loss, the principle of the system was analyzed and the closed rotary system was designed. Through model building,theoretical calculation and AMESim simulation for the closed rotary system,the simulation curves of the closed rotary system of excavator were obtained.It is verified that the closed system can save 1 195.5 kJ than the open system.