The invention provides a pressure-stabilizing, liquid-supplementing and gas-exhausting device of a closed liquid cooling system. The pressure-stabilizing, liquid supplementing and gas-exhausting device of the closed liquid cooling system comprises an air-cooling liquid heat exchanger, a load heating element, a liquid storage tank, a liquid supplementing pump, a spiral micro bubble separator, an electric heating water tank, an expansion tank, a liquid supplying pump, electromagnetic valves, ball valves, and a stop valve. The pressure stabilization, the liquid supplement and the gas exhaust of the closed liquid cooling system are achieved by the liquid supplementing pump, the first electromagnetic valve, the second electromagnetic valve, the second ball valve, the third ball valve, the fourth ball valve, the fifth ball valve and the sixth ball valve, in association with the spiral micro bubble separator. The pressure-stabilizing, liquid-supplementing and gas-exhausting device of the closed liquid cooling system is low in cost and convenient in operation. The pressure-stabilizing, liquid-supplementing and gas-exhausting device of the closed liquid cooling system is of a great practical value.