A water cooling system includes a temperature control device which is connected with a first heat exchanger. A second heat exchanger includes a water temperature control path and a constant temperature water path. The water of the first heat exchanger is controlled by the temperature control device and flows to the water temperature control path. The water in the constant temperature water path tows through the second heat exchanger to proceed heat exchange with the water in the water temperature control path, and then flows to the target equipment. The temperature difference of the water flowing to the target equipment is smaller than that of conventional water cooling system.
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