Using forward and backward finite difference algorithm, the electronic states of InAs/GaSb/AlSb active region structure of antimonide cascade laser were calculated and analyzed theoretically in this paper. The effects of Hamiltonian operator order, effective mass parameter modification, internal interface state on the energy state and wave function were studied. The analyses show that the positive value of the effective mass parameter of the conduction band can effectively inhibit the generation of spurious solutions under two operator orders, and the transition energy under Burt-Foreman operator order is more reasonable. For the internal interface with the slow-change assumption, the calculated value of the transition energy is slightly higher than that of the steep interface, and the wave function profiles of the two are similar near the interface.