We study superlattices in non-uniform electric field to obtain mid infrared laser. We exploit the transfer matrix method and the transmission coefficient to find the suitable parameters that lead to resonant energy levels that are appropriate for generating three and four-level
laser. In particular, we consider superlattice of GaAs/Al0.45Ga0.55 As consisting of four barriers, and we apply a graduated electric field. Our calculations predict that under the effect of the electric field equal to 10KV/cm and its graduation step equals to 1.26 KV/cm with the condition of the transition resonant with LO phonon, the obtained electronic transitions are shown to have wavelengths of 23.49 µm and 32.15 µm. We found that the variation of the electric field has an influence on the energy profile of the electron in the superlattice.