Abstract: To explore the effect of Parahydrogen–Orthohydrogen(P-O) conversion applied to vapor-cooled shield on the insulation performance of liquid hydrogen storage tanks, a two-dimensional VD-MLI/VCS model with a P-O adiabatic conversion chamber was established. The heat transfer law and insulation performance of the composite insulation structure were analyzed from multiple perspectives. The results show that the optimal insulation efficiency is achieved when the P-O conversion chamber is arranged at 50% of the VCS pipe length, with a heat leak of 0.101 W·m⁻², which is reduced by 7.17% compared to not setting the P-O conversion chamber. In the thermal insulation design, adjusting the VCS position can reduce the heat leak by 54.17% at most, which is more significant than adjusting the position of the P-O conversion chamber. Along the flow direction of the cryogenic hydrogen gas, the heat leak first increases, then decreases, and then continues to increase. The conversion chamber improves the insulation performance on the outlet side of VCS, making the insulation performance of various parts of the storage tank more consistent. This study provides more accurate research tools and results support for the design of composite insulation structures for liquid hydrogen storage tanks.