A seawater circulation system for a ship, the seawater circulation system comprising: a sea chest for pumping seawater from sea; a cooling unit coupled to the sea chest to receive the seawater from the sea chest, and partially coupled to a heat generation body to lower a temperature of the heat generation body through heat exchange; a scrubber unit for treating an exhaust gas generated in the ship; a first discharge pipe unit for discharging the seawater discharged from the cooling unit to an outside; a supply pipe unit coupled to the first discharge pipe unit and the scrubber unit to supply a part or all of the seawater discharged from the cooling unit to the scrubber unit; a second discharge pipe unit coupled to the scrubber unit and the first discharge pipe unit to discharge the seawater from the scrubber unit to the first discharge pipe unit; a first pump provided in the cooling unit to pump the seawater from the sea chest; wherein a first valve for adjusting a flow rate is provided between the first discharge pipe unit and the supply pipe unit; characterized by comprising a circulation pipe unit having both ends coupled to the cooling unit, which is located between the first pump and the heat generation body, to allow the seawater to circulate therethrough, wherein the circulation pipe unit is at least partially located inside or outside the first discharge pipe unit to lower a temperature of the seawater located in the first discharge pipe unit, and has a flow path which is smaller than a flow path of the cooling unit to receive a part of the seawater located in the cooling unit, wherein a second valve for adjusting a flow rate is provided between the circulation pipe unit and a main pipe of the cooling unit, wherein depending on a state of the second valve, communication between the main pipe and the circulation pipe unit is opened or blocked. a sea chest for pumping seawater from sea; a cooling unit coupled to the sea chest to receive the seawater from the sea chest, and partially coupled to a heat generation body to lower a temperature of the heat generation body through heat exchange; a scrubber unit for treating an exhaust gas generated in the ship; a first discharge pipe unit for discharging the seawater discharged from the cooling unit to an outside; a supply pipe unit coupled to the first discharge pipe unit and the scrubber unit to supply a part or all of the seawater discharged from the cooling unit to the scrubber unit; a second discharge pipe unit coupled to the scrubber unit and the first discharge pipe unit to discharge the seawater from the scrubber unit to the first discharge pipe unit; a first pump provided in the cooling unit to pump the seawater from the sea chest; wherein a first valve for adjusting a flow rate is provided between the first discharge pipe unit and the supply pipe unit; characterized by comprising a circulation pipe unit having both ends coupled to the cooling unit, which is located between the first pump and the heat generation body, to allow the seawater to circulate therethrough, wherein the circulation pipe unit is at least partially located inside or outside the first discharge pipe unit to lower a temperature of the seawater located in the first discharge pipe unit, and has a flow path which is smaller than a flow path of the cooling unit to receive a part of the seawater located in the cooling unit, wherein a second valve for adjusting a flow rate is provided between the circulation pipe unit and a main pipe of the cooling unit, wherein depending on a state of the second valve, communication between the main pipe and the circulation pipe unit is opened or blocked.