The five low-lying configurations of CH3C(O)OSSOC(O)CH3 are studied by ab initio calculations by B3LYP, MP3 and MP4 methods with Aug-cc-pVDZ basis set. Their rotational constants and dipole moments of these five configurations are determined. The vertical ionization energies of the configurations, calculated with electron propagator theory in the P3/6-311++G(2d,2p) approximation, are in agreement with the experimental data from photoelectron spectroscopy. The relative energies of the configurations and the comparison between the simulated and the experimental photoelectron spectra demonstrate that there are at least two configurations of CH3C(O)OSSOC(O)CH3 in the gas-phase experiments. The geometrical parameters of five lowest-lying configurations are optimized in the cationic state and compared with those of the neutral configuration. Remarkable structural relaxations after ionization are found, especially for the dihedral angles D(C2O4S5S10) and D(O4S5S10O9).