CH₃NH₃SnI₃ perovskite is an interesting compound for optoelectronics applications. In this paper, we report the results of our investigations on the electronic and optical behavior of this structure by density functional theory. The calculations were performed using PW-LDA, GGA (PBE) and GW approximations. The band-gap values obtained by GGA (1.02 eV) is bigger than that obtained by LDA (0.77 eV) and the best band gap value for the CH₃NH₃SnI₃ perovskite obtained by the GW approximation (1.38 eV), which is close to the experimental value. The calculated total- and partial density of states for this perovskite show that the Sn and I atoms has a direct effect on the electronic properties of this atomic compound. The results obtained on optical properties such as the low reflectivity rate and high absorption of the incident photon energy in 1.5–3 eV energy range indicate the CH₃NH₃SnI₃ has a good optical property to absorb solar wavelengths as an active layer in the perovskite-based solar cells.