The energy levels of magnesium_like ion Cu ⅩⅧ in n=3complex configurations are computed by multi_configuration Hartree_Fock with relativistic corrections (HFR) method.The Slater parameters are optimized with the least_square_fit(LSF) technique based on the available experimental data.With these new parameters, th e wavelengths,oscillator strengths and transition probabilities for transitions 3s2—3s3p,3s3p—3p2,3p2—3p3d,3s3d—3p3d,3p3d— 3d2 in n=3complex configurations for magnesium_like Cu Ⅹ Ⅷ are predicted.