In this paper a detailed simulation and theoretical analysis based on model-solid theory and the k.p method are presented to investigate the dependence of the band structure on the strain deformation in a novel type-II quantum well (QW) heterostructure InAs_{1-y}Sb_{y}/Ga_{x}In_{1-x}Sb under the uniaxial approximation, and subsequently the optical transition and the gain in the interband cascade lasers containing it have been evaluated with unchanged injection current densities. The simulation results show that the strain effect on the transition in this heterostructure will not behave as a simple monotonic trend with the lattice mismatch of InAs_{1-y}Sb_{y}/Ga_{x}In_{1-x}Sb interface, but as a function of the complex strain chain including the whole active region. It is important to the subsequent device design and optimization.