The relationship between the optical spectra and the crystal structure parameters is set up,and the local structure parameters of group [Ni(H₂O)₆]²⁺ of Ni₂CdCl₆·12H₂O crystal can be determined from the optical spectra at 14 K. The local structure and absorption spectra of Ni²⁺ ions of Ni₂CdCl₆·12H₂O crystal are interpreted based on superposition model and the complete diagonalization procedure method. According to the calculation,the local structure values of [Ni(H₂O)₆]²⁺ are: bond length R ≈ 0.2009 nm and bond angle θ ≈ 55.1°. Theoretical results of optical spectra are in good agreement with experimental findings.