This paper presents the theoretical investigation of energy of core levels (CL) of the ferroelectric SbSBr single crystals in paraelectric and ferroelectric phases. Since the best approximation for the CL levels is a calculation by the Hartree-Fock method, the molecular model of SbSI crystal was used for calculations. It was found that CL of this semiconductor ferroelectric are sensitive to the small lattice distortion at phase transition, and on ion charges. The experimental splitting of CL obtained by XPS was compared with theoretically calculated one by two different methods. The cluster model calculations showed that the splitting of the CL in SbSBr might be caused by photoelectron emission from the atoms, which have different ion charges at the surface.