Perovskites CsSnX3 (X = Cl, Br and I) are promising for photovoltaic cells and other energy store devices, having high stability and less toxicity (lead free). The present work explored the structural, electronic and optical properties of these perovskites in different phases using generalized gradient approximation (GGA) and modified Becke-Johnson (TB-mBT) techniques. The structural properties of this system depend on temperature variation and selection of halogens, which changes the electronic and optical properties. The calculated structural parameters (lattice constants, bulk modulus, volume, bond length and bond angles) are in good agreement with the experimental values. The results presented in this article confirm that these compounds have direct band gaps, lie in the visible region (1.3–2.9 eV), hence they are more suitable candidates for optoelectronic devices. This study covers the lack of theoretical work concerned to these systems.