The reactions of Mn+ (S-7, S-5) with CS2 have been studied at the B3LYP/TZVP level on both septuplet and quintet potential energy surfaces (PESs). The overall energies have been refined at the CCSD (T) level. The calculated results indicate that the reactions of Mn+(S-7, S-5) with CS2 proceed via an insertion-elimination mechanism. Calculations show that the quintet reaction is more favorable than the septuplet under high energy conditions. The spin-forbidden reaction Mn+ (S-7) + CS2 -> MnS+ ((5)Pi) + CS proceeds through a septuplet-quintet surface and the crossing seam is approximately determined All results have been compared with the existing experimental and theoretical data.