The calculation of the energy displacement of excitonic lines due to elastic strain of DSB have been performed for wurzite type crystals using the deformation potential theory. It is shown that nonlinear dependence of the position of valence bands on lattice strain gives rise to a different behavior of excitonic lines for various types of dislocation. The results of calculations are applied for the explanation of the characteristics of the free exciton reflection spectra and the spectra of photovoltaic effect in CdS. The qualitative agreement between theory and experiment is demonstrated for both phenomena.