Abstract: In this study, the effect of the type-Ⅰ band on the performance of HgCdTe-based nBn devices was analyzed theoretically. A theoretical calculation of the relationship between the composition and doping concentration of the barrier layer and the band offset was obtained, and the relationship between the doping concentration of the absorption layer and the dark current of nBn LWIR HgCdTe devices was determined. Both the doping concentration and composition gradient between the barrier and absorption layers of nBn LWIR HgCdTe devices were optimized. A two-dimensional device simulation model was established, and the band structure of nBn LWIR HgCdTe devices was calculated. The results show that optimization of the device structure parameters effectively reduced the turn-on voltage required for device operation, while almost no depletion region was formed in the absorption layer, which effectively inhibited the SRH generation-recombination current and tunneling current. In this study, we also calculated the temperature-dependent dark current of optimized nBn LWIR HgCdTe devices; the operating temperature of the device was above 110 K. This study establishes a theoretical basis for developing high-performance barrier-structured LWIR-HgCdTe devices.