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. <EOS>