The invention relates to a water cooling system of internal and external cycle switching for adapting for water surface clean ships in different water areas. The water cooling system comprises an external circulation unit, an internal circulation unit, a first control valve, a second control valve, a third control valve and a fourth control valve, wherein the external circulation unit comprises aseawater tank, a water inlet pipeline used for enabling the seawater tank to communicate with a main machine, a water pump, and a drain pipeline; the internal circulation unit and the external cycle unit can be switched for use, and the internal circulation unit comprises a fresh-water tank arranged on a ship body and constituting a pressure-loading chamber, a fresh-water pipeline used for enabling a fluid outlet pipe of the fresh-water tank to communicate with the water inlet pipeline, and a bypass branch pipe used for enabling the drain pipeline to communicate with a backflow pipe of the fresh-water tank; and the first control valve, the second control valve, the third control valve and the fourth control valve are arranged on the water inlet pipeline, the drain pipeline, the fresh-waterpipeline and the bypass branch pipe. According to the water cooling system, through the switching use of the internal circulation unit and the external circulation unit, the cooling of a cooler of the main machine is guaranteed, and the water cooling system is applicable to the different water areas with clear water quality and muddy water quality.