The present disclosure provides a cooling system of an emergency cooling tank, which enables long-term cooling without refilling cooling water, in case of the change in a quantity of heat transferred to the emergency cooling tank according to a lapse of time upon an occurrence of an accident of a nuclear reactor, and a nuclear power plant having the same. The emergency cooling tank cooling system includes an emergency cooling tank, a heat exchanging device installed to be exposed to an outside of the emergency cooling tank to operate in air, and configured to externally emit such that the operation of the emergency cooling tank is continued even without refilling the cooling water, and an opening and closing unit installed at an upper portion of the emergency cooling tank to be located higher than a water level of the cooling water.