The spectral fine structure, zero-field splitting parameters (D, a-F), crystal structure in Al2O3∶Fe3+ crystals were studied with the 252 ranks completely diagonalized Hamiltonian matrix of the 3d5 configuration in trigonal symmetry with irreducible algorithm and group theory. The results show that the contribution of spin quartet state on the ground-state energy levels is the most important, and the contribution of spin doublet state is small but cannot be neglected. The calculated results are in good agreement with the experimental results. The influences of spin-orbit interaction and spin-spin interaction on the spectra fine structure and zero-field splitting parameters were further studied, and the influence of spin-orbit interaction is dominant, but the influence of spin-spin interaction cannot be neglected.