With the strong-field scheme and cubic bases, the complete d3 energy matrix in a tctragonally distorted cubic-field has been constructed. By diagonalizing this matrix, the energy spectra of Sr TiO3 :Cr3+ and Sr TiO3 :Mn4+ at normal pressure and various temperatures have been calculated. Correspondingly, the FORTRAN program calculating the g factor of the ground state has been worked out. By using the program and the wavefunction obtained from diagonalizing the complete energy matrix, the g factors of the ground state of SrTiO3 :Cr3+ and SrTiO3 :Mn4+ at normal pressure and room temperature have been evaluated. The calculated results are in good agreement with the optical spectral and EPR experimental data. The comparison and analysis of the results of two crystals have been made. It is demonstrated that the covalency of the bonding between Mn4+ and ligands (O2 ) in SrTiO3:Mn4+ is stronger than the one of the bonding between Cr3+ and ligands (O2 ) in SrTiO3:Cr3+. It is shown that the obtained wavefunctions and values of parameters are reasonable.