The complex potential energy surface for the ion-molecule reaction of the silaformyl anion (HSiO-) with carbon disulfide (CS2) is theoretically investigated at the B3LYP/6-311++G(d,p) level. Possible reaction channels leading to five low-lying products (a) HSiOS- + CS, (b) HCS2- + SiO, (c) HSiS- + COS, (d) HCOS- + SiS, and (e) HSiS2- + CO are probed. It is shown that all the five products are both thermodynamically and kinetically accessible via various reaction pathways involving the ion-molecule complexes and three-membered ring and four-membered ring intermediates. The calculated results significantly differ from previous experimental observation for the reaction HSiO- + CS2 that only the two products (a) and (b) were characterized, yet are in harmony with the experimental results for the isotopically labeled reaction (HSiO-)-O-18 + CO2. The large discrepancies between the theoretical and experimental results suggest that further experiments on the reaction HSiO- + CS2 may be in great need. Our calculations may provide a useful guide for further identification of the three hitherto experimentally unobserved products (c), (d), and (e). Furthermore, the present mechanistic theoretical study may give some valuable information for other analogous ion-molecule reactions such as CH3SiO-, CH3OSiO-, HSiS-, and HSiNH- with CO2, COS, and CS2.