Abstract: The low-temperature liquid nitrogen filling system is taken as the research object. Through FLUENT simulation and experimental study,the results show that the numerical simulation match well with the experimental results. The temperature of the small flow pre-cooling liquid nitrogen increases by about 5 K,a certain degree of subcooling and a low heat leakage rate play an important role in single-phase filling.Taking the cryogenic liquid storage bottle as the research object,the filling process is simulated and tested. The results show that the liquid level in the initial stage of filling is lower than the critical liquid level. Internal convection heat exchange,bubbles are formed in the liquid phase,part of the gas phase is liquefied for the second time,and there is no temperature stratification in the bottle. In the middle and later stages of filling,the gas-liquid interface tends to be stable,there are no obvious bubbles in the liquid phase,and no obvious bubbles in the gas phase. The secondary liquefaction and the temperature gradually formed stratification. The liquid nitrogen evaporation rates of the numerical simulation and experiment were about 1.7% and 1.5%,respectively,with good consistency. Based on the experience of liquid nitrogen analysis,the simulation prediction of the“filling process”of liquid hydrogen is carried out. The results show that the liquid phase rate and temperature in the liquid storage bottle during liquid nitrogen and liquid hydrogen filling process have similar variation laws. Hydrogen refueling has certain reference significance.