The completely diagonalized Hamiltonian matrixes of order 45 of 3d2/3d8 ion configurations in the trigonal symmetry sites were established by means of crystal field theory and irreducible representation method. The Hamiltonian matrixes include four kinds of microscopic magnetic interactions: spin-orbit interaction, spin-spin interaction, spin-other-orbit interaction and other-orbit-other-orbit interaction. The spectral fine structure and crystal local structure of Ni2+∶α-Al2O3 crystal were calculated by the Hamiltonian matrixes. Meanwhile, the four kinds of interactions and their effects to the spectral fine structure and the Jahn-Teller effect were also analyzed. The calculated values were conformed with the experimental values. The results show that doping Ni2+ ions cannot change the symmetry, and it was discovered and explained the existence mechanism of Jahn-Teller effect in spectral fine structure of α-Al2O3 doped with Ni2+.