The ultracold neutron (UCN) transport code, MCUCN, designed initially for simulating UCN transportation from a solid deuterium ( \({\text{SD}}_{2}\) ) source and neutron electric dipole moment experiments, could not simulate UCN storage and transportation in a superfluid \(^{4}{\text{He}}\) (SFHe, He-II) source accurately. This limitation arose from the absence of an \(^{4}{\text{He}}\) upscattering mechanism and the absorption of \(^{3}{\text{He}}\) . And the provided source energy distribution in MCUCN is different from that in SFHe source. This study introduced enhancements to MCUCN to address these constraints, explicitly incorporating the \(^{4}{\text{He}}\) upscattering effect, the absorption of \(^{3}{\text{He}}\) , the loss caused by impurities on converter wall, UCN source energy distribution in SFHe, and the transmission through negative optical potential. Additionally, a Python-based visualization code for intermediate states and results was developed. To validate these enhancements, we systematically compared the simulation results of the Lujan Center Mark3 UCN system by MCUCN and the improved MCUCN code (iMCUCN) with UCNtransport simulations. Additionally, we compared the results of the SUN1 system simulated by MCUCN and iMCUCN with measurement results. The study demonstrates that iMCUCN effectively simulates the storage and transportation of ultracold neutrons in He-II.
