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In this paper we establish the high-order perturbation formulas of zero-held splittings D and E and g factors g(x), g(y) and g(z) for 3d(3) ions in rhombic symmetry by using a two-spin-orbit (SO) coupling parameter model, in which not only the contribution due to the SO coupling of the central 3d(3) ion but also that of the ligands are included. Based on these formulas, all five EPR parameters for the Cr3+ ion at the rhombic defect site in the cubic AgCl crystal are satisfactorily explained by considering suitable defect-induced lattice distortion. The relative importance among the various contributions to the EPR parameters from the SO couplings of the central 3d(3) ion, the ligand ions and the mixed ones is discussed. It can be seen that for the 3d(3) ions in crystals with ligands having large SO coupling parameter, the contribution due to the SO coupling of ligands cannot be neglected and we should apply the two-SO parameter model in studies of EPR parameters.