The utility model discloses an energy conservation system of a machine room, which comprises two rows of server machine cabinets which are arranged back to back and an air conditioner set. A thermal channel for hot air flow to pass is formed between the backs of the two rows of the server machine cabinets and communicated with an air inlet of the air conditioner set through an air return path, the upper portion of the thermal channel is provided with a heat exchanger which is communicated a natural water cooling device arranged outdoors through a water pipe and a water pump to form a cooling water circulation loop. Two ends of the thermal channel are respectively provided with windproof blocking plates which form a closed space with the lower end face of the heat exchanger, the backs of the two rows of server machine cabinets and the floor. The upper portion of the heat exchanger is provided with an air return branch path connected with an air return pipeline in a sealing mode, and an air return fan is arranged in the air return branch path. Large-scale modification of the data center machine room is avoided, natural cooling resources are fully utilized by arranging the natural water cooling circulation loop, loads of an air conditioner system is lowered, and energy consumption of the air conditioner system is saved to the maximum extent.