Abstract The possible geometrical structures and relative stabilities of silicon–sulfur clusters (SiS 2) n + (n=1–5) are explored by means of DFT quantum chemical calculations. The effects of polarization functions and electron correlation are included in these calculations. The electronic structure and vibrational spectra of the most stable geometrical structures on each (SiS 2) n + potential energy surface are analyzed by the same method. As the result, the regularity of the (SiS 2) n + cluster forming is obtained that is the most stable structure of SiS 2 + is with D ∞h symmetry, and (SiS 2) n + (n=2–5) have tetra-atomic rings of Si and S atoms bound alternatively, and the rings are perpendicular to each other. The calculation may predict the mechanism of the (SiS 2) n + cluster forming is based on the bonding of Si and S atoms with SiS 2 + as the core and SiS 2 as the building block, forming tetratomic ring molecular chain with rings perpendicular to each other.