Abstract: The reaction mechanism for dehydrogenation of silathione H_2SiS was studied by means of intrinsic reaction coordinate (IRC) method. The reaction ergodography was analyzed by ab initio MO calculations using RHF/4-31G basis set. The equilibrium structure of H_2SiS which has C_(2υ). symmetry was optimized.The bond lengths of Si-S and Si-H are 0.2018 nm and 0.1484 nm, respectively. The bond angle of HSiS is 125.3°. The transition state was also located which has C_3 symmetry. The bondlengths of Si-S, Si-H_1 and Si-H_2 are 0.2045 nm, 0.1860 nm and 0.1522 nm, respectively. The bond angles of H_1SiS and H_2SiS are 105.0° and 147.4°, respectively. The activation energy was calculated to be 396.4 kJ·mol~(-1) and the reaction heat is 210.0 kJ·mol~(-1). The change of some physical properties along IRC were presented. At the same time, the vibrational analyses of the reactant and the transition state have also been done. At last, the frequency factor A of the reacton and the entropy of activation at 500 K were calculated with the application of RRKM theory. The results of H_2SiS were compared with its carbon analogy; thioformaldehyde CH_2S.