The electronic structures of the perfect CsI crystal and the crystal containing iodine vacancy and F, F2 color centers are studied within the framework of the fully relativistic self-consistent Dirac-Slater theory, by using a numerically discrete variational (DV-Xα) method. Calculated results reveal that the existence of the iodine vacancy results in the band gap widening and does not introduce the new energy level in the forbidden band. However, the crystal containing F color centers and F2 color centers have their donor energy levels introduced in the forbidden band. The transition energy from energy level of F color center and F2 color center to the bottom of conduction band is 169 eV (736 nm) and 115 eV, respectively, which are consistent with the experimental results. This result indicates that the 750 nm absorption band originates from the F color center and the 11 eV absorption band originates from F2 color center.