Abstract: The quantificational relationship between EPR zero-field splitting parameter D and structure parameters of
Cr³⁺ vacancy centre in CsCdF₃:Cr³⁺ crystals was established according to the superposition model and third-order perturbation theory. The
existence of Cd²⁺ vacancy and the lattice distortion were verified. Meanwhile, F^- ion moving toward the central Cr³⁺ ion by X₁=0.00291nm,
X₂=0.001nm, X₃=0.00262nm was obtained. Good agreement between the theoretical results and the experimental values shows that the assumption of
the Cd²⁺ vacancy and the lattice distortion is reasonable. Although the main of source of the tetragonal crystal field comes from the Cd²⁺
vacancy caused by the charge compensation, the contribution of the lattice distortion can not be neglected.