Abstract: Aiming at the problems of high cost, limited supply and high safety risk of liquid hydrogen in the detection of thermal insulation performance of liquid hydrogen cylinders, according to the thermal insulation structure and heat leakage mechanism of liquid hydrogen cylinders, the theoretical derivation and experimental research on the ratio of liquid hydrogen to liquid nitrogen evaporation rate were carried out from the aspects of theoretical basis, evaporation rate conversion method and influencing factors of liquid nitrogen instead of liquid hydrogen detection technology. Taking 1 m³ liquid hydrogen cylinder as the research object, the evaporation rate comparison test was carried out by using liquid hydrogen and liquid nitrogen respectively. The results show that the ratio of liquid hydrogen evaporation rate to liquid nitrogen evaporation rate was 2.68~4.60 when the filling rate was less than 40.5%, and the ratio was positively correlated with the filling rate at low liquid level. The conversion value of evaporation rate when the filling rate was 50% was obtained by further fitting, which was basically consistent with the theoretical derivation results. It provided preliminary data support and reference for liquid nitrogen instead of liquid hydrogen to carry out thermal insulation performance testing.