In this work, a series of potential energy surfaces (PESs) of S2O was constructed in order to get the most accurate ab initio band origins of this massive molecule. The convergence of the coupled cluster energies with respect to both basis set size [aug-cc-pCVXZ, X=T, Q, 5, and 6] and the order of the excitation [CC(n), n = 2, 3, and 4] was analyzed. For the first time, the band origins of 32 S2 16(18) O were variationally calculated with the error of 0.5 cm-1 using the ab initio PES. The vibrational energies of the most abundant six isotopologues of S2O were predicted.