By means of a complete configuration mixing unified crystal field theory for d⁸(D_4h^*),the optical spectra,the ground state ZFS,EPS parameters,the ground state paramagnetic susceptibility and the magnetization of the Ni(mpz)₄Cl₂ compounds are analysed and calculated systematically.Numerical results agree well with the experimental data,so a complete and reasonable explanation is provicled for the magnetic of Ni(mpz)₄Cl₂ compounds.