The band structure of InAs/GaSb superlattice was calculated using K.P theory under the envelope-function approach. The electro effective mass and absorption coefficient with different material structure were also calculated. Four-layer structure model considering two interfaces was investigated and used to modify the calculation. Comparing with the experiment results, this four layer model has closer cutoff wavelength than standard model. The results showed that different interface structure can also influence the band structure, leading to the changes of cutoff wavelength. For the same InAs/GaSb superlattice material fully compensated with InSb interface, one with symmetric InSb interfaces has shorter cutoff wavelength than superlattice with asymmetric interfaces.