Abstract: Hydrogen molecules have two isomers,namely orthohydrogen and parahydrogen.Due to the difference in rotational energy levels,the conversion process from parahydrogen to orthohydrogen accompanies endothermic effects.Integration of a para-ortho hydrogen converter to the vapor cooling shield of a liquid hydrogen storage tank enables addi-tional cooling capacity other than the sensible heat of the vented gas,which further reduces the evaporation loss and conse-quently extends the storage life of the liquid.In order to quantitatively evaluate the insulation performance and the influ-encing factors,a system-level model for the liquid hydrogen tank containing a vapor cooling shield,a multilayer insulation materials,and para-ortho hydrogen converters has been established.The cooling effect of the para-ortho hydrogen conver-sion and the heat transfer process during the venting process was studied.The effects of position and quantity of the paraortho hydrogen converters and the thermal boundary temperature on the cooling power were investigated.The general be-havior of the para-ortho hydrogen conversion cooling effect and its contribution to the insulation performance of the vapor cooling shield is presented.