Infrared photodetectors are useful for a variety of military and civil applications, such as space science, military equipment, industrial production and so on. Presently, infrared photodetectors are developing towards high performance and low cost to meet the technical requirements. Compared to single color detectors, dual-band infrared detectors covering different atmospheric windows allow for simultaneous acquisition of target information in both wavelengths which is the most obvious advantage. Therefore, the dual-band capability of the detector makes it possible to discriminate between different temperatures and objects, improving the accuracy of temperature measurement and target recognition. Complex infrared backgrounds can be suppressed and it is possible to reduce the false alarm rates significantly in early warning, searching and tracking systems. Mid-long wavelength dual-band infrared detectors based on type II superlattice have great advantages in terms of cost and performance, and have become a popular research topic in the field of new infrared detectors. However, infrared detectors need to reduce dark current density and crosstalk to achieve better performance. The nBn superlattice detector has a unique band gap engineering approach, which can work at a higher temperature and has better thermal stability compared to traditional single color detectors. This leads to better performance and longer operating life in harsh environments. Additionally, the nBn structure has a high absorption coefficient, resulting in a high detectivity and low noise. However, the development of nBn superlattice dual-band detectors faces several challenges, such as the difficulties in fabrication and the limitations in performance. The fabrication of the nBn structure requires precise control of the layer thickness and doping levels, which is a complex process. Besides, the performance of the nBn detector is limited by dark current and temperature. These issues need to be addressed through further research and development. To this end, the paper designs an InAs/GaSb superlattice mid/long dual-band infrared detector with nBn structure to reduce dark current density and crosstalk by simulation of silvaco.The materials of the mid-band and the long-band absorber are selected by calculating the band gap of InAs/GaSb using the k.p model to meet the requirements of the design objectives. The mid/long dual-band infrared detectors model with nBn structure is eatablished by silvaco, and the responsivity and dark current density values of the mid/long waveband channels are compared by simulating some device structures at different bias voltages. The effects of the barrier layer thickness, absorber layer thickness, and doping in different regions are analyzed to obtain the best model parameters to reduce the dark current density and crosstalk.By modeling and simulating the nBn type II superlattice mid/long dual-band infrared detector structure, the thickness of the absorber and barrier layers and the doping concentration are optimized to reduce the dark current and the crosstalk in the mid-band and the long-band channel. At 77 K, the cutoff wavelengths of the dual-band detector are 4.8 µm （50%） at 0.3 V and 10.5 µm （50%） at -0.3 V (Tab.8) with the detectivies of 3.9×10¹¹ cm·Hz^1/2W^-1 and 4.1×10¹¹ cm·Hz^1/2W^-1 (Tab.9). The dark current density is 4×10^-5 A·cm^-2 and 1.3×10^-4 A·cm^-2 respectively (Tab.7). This provides a theoretical basis for subsequent material growth and device processes. The advantages of the designed superlattice mid/long dual-band infrared detector are simple device structure, low dark current density, and similar detection rate compared with the foreign InAs/InAsSb infrared detectors based on nBn structure and domestic InAs/GaSb infrared detectors based on PπMN structure. The simulation performance will have some differences with the actual device performance, so the subsequent material growth and device process will be carried out to further feedback the simulation, and the device structure will be further improved.