Based on the analysis of group-chain scheme wavefunctions and the use of the constraint condition set down by the ratios of crystal-field parameters calculated by the point-charge model, the crystal-field-level fitting and the study of Zeeman interaction characterized by the g-factor in have been carried out, in which the ions occupy positions with point symmetry . The RMS of energy-level fitting is less than , and the corresponding wavefunctions of Stark sublevels are useful in the calculation of the g-factors of the ground and excited states. The calculated results agree well with the experiment and confirm Karayianis' partial g-sum rule. The method proposed turned out to be effective in the study of not only the spectroscopic and laser properties but also the magnetic properties of rare-earth ions in crystals.