The invention discloses an exhaust cooling capacity utilization system of a space liquid hydrogen storage tank. The exhaust cooling energy utilization system comprises a compressor, a buffer tank, a throttle valve and a gas-liquid separator which are connected with a gas outlet of the space liquid hydrogen storage tank in the flow direction of working media in sequence; a liquid outlet of the gas-liquid separator communicates with a liquid inlet of the space liquid hydrogen storage tank through a pipeline with a check valve in one way, and a gas outlet of the gas-liquid separator is connectedwith an inlet of an evaporator; and an outlet of the evaporator is connected with an inlet of the compressor. According to the exhaust cooling energy utilization system, by utilizing hydrogen gas cooling capacity generated during heat evaporation of the liquid hydrogen storage tank, part of liquid hydrogen is recycled, and the remaining gas hydrogen cooling capacity is used for cooling the exterior of the liquid hydrogen storage tank; environmental heat leakage is eliminated, and the working time of a precooling mechanism is shortened; the energy consumption of the system is reduced, and the system efficiency is improved; and meanwhile the exhaust cooling capacity utilization system benefits improvement of reliability of the liquid hydrogen storage tank.