The structures, energetics, spectroscopies, and isomerization of singlet and triplet SiC2S isomeric species are explored at various levels. At the B3LYP/6-311G(d) level, a total of 29 minimum isomers and 37 interconversion transition states are located. At the higher CCSD(T)/6-311+G(2df)//QCISD/6-311G(d)+ZPVE level, the lowest lying isomer is the linear SiCCS (1)1 with a resonance structure mainly between Si=C=C=S and SidropC-CdropS. In contrast to the C3S molecule that has no kinetically stable singlet species besides CCCS, SiC2S has another two kinetically very stable species, i.e., the SiCC three-membered ring with exocyclic SSi bonding (1)5 at 23.2 kcal/mol, and the SiCSC four-membered ring with CC cross bonding (1)7 at 44.3 kcal/mol. Particularly, isomer (1)5 possesses considerable SidropS and CdropC triple bonding character and can be viewed as a charge-transfer species containing SiS+ and C-2(-) Isomer (1)7 has a very short CC crossed bond due to the existence of two sets of pi-bonding orbital and the weak electron-accepting ability of silicon. The remaining singlet and all the triplet species except triplet SiCCS (3)1 either have much higher energy or much lower kinetic stability and have little chance of existence. The bonding nature and possible formation strategies of (1)1, (1)5, and (1)7 are discussed.