Abstract: The energies,equilibrium geometries and harmonic frequencies of the ground state X1Σg+,the second state B1Σu+ and the third degenerate state C1Πu of molecule T 2 have been calculated using the method Group Sum of Operators of SAC/SAC-CI with the basis sets D95++**,6-311++g** and cc-PVTZ.Comparing the three basis sets above mentioned,the conclusion was gained that the basis set cc-PVTZ was the most suitable for the energy calculation of molecule T 2.The whole potential curves for these three electronic states were further scanned adopting SAC/cc-PVTZ method for the ground state and SAC-CI/cc-PVTZ method for the excited states,then a least square was fitted to Murrell-Sorbie function,and last the spectroscopy constants were calculated,which are in better agreement with the experimental data.It was believed that Murrell-Sorbie function form and SAC/SAC-CI method were suitable not only for the ground state,but also the low-lying excited states.