This article deals with the low-lying electronic states——the charge transfer excitons(CTE), of alkali halide crystals. By the standard perturbation method of degenerate states, the energy spectra of the CTE are studied and the effective Hamiltonian of the CTE system is derived. The energy levels of the CTE obtained by numerical calculations agree with the peak positions of light absorption spectra found in the literature, the relative errors are small. In this article, the bandwidth and the effective transla-tional mass of the CTE are also obtained.