A split cooling system of an internal combustion engine may include a water pump configured to circulate cooling water; a cylinder head and a cylinder block configured to be supplied with the cooling water from the water pump; an integrated flow control valve configured to include an inlet provided to be supplied with the cooling water of the cylinder head and a plurality of valves that are configured to be opened or closed to distribute the cooling water introduced through the inlet to an oil heat exchanger, a heater core, and a radiator; and a split cooler configured to be mounted at the cylinder block to provide a split cooling channel in the cylinder block and the cylinder header.