In the presented work, a theoretical study of the effect of β-FeSi2 lattice deformation on the type and magnitude of the first transition in the electronic band structure was carried out. Images of nanocrystallites obtained using high-resolution transmission electron microscopy were used as a source of deformation data. All in all, 137 variants of β-FeSi2 lattice deformation were considered in the work. Six types of first transitions different from the first transition in unstrained β-FeSi2 were discovered. The values of the first transitions from 0.02 to 0.64 eV (direct) and from 0.01 to 1.12 eV (indirect) were obtained.