A theoretical method for studying the local lattice structure of 3d(3) ions in tetragonal ligand-field is presented. The formulas relating the crystal structure parameters with optical spectrum and electron paramagnetic resonance have been derived by using Zhao's Semi-SCF d-orbit Wave Functions model, Point-charge Crystal Field model, and Perturbation Loop Method. This theoretical system is applied to calculate the local distortion structure of CsCl: Cr3+ crystal at 293 and 77 K. The calculated results are accorded well with the experimental values.