Abstract: The structures and stability of triplet HFSiS system were investigated by density functional theory（DFT）in detail. The optimized geometrical parameters and vibrational frequencies of all species were obtained at the level of B3LYP/6-311G** and the assignments of them were performed. At the same theoretical level, IRC calculations were carried. In addition, the singlet-point energies and relative energies were calculated by high level electron-correlation CCSD（T）/6-311G**. The isomerized and dissociated processes were explained by vibrational mode analysis method. The triplet PES is compared to the singlet one. The results are as the following: there are six isomers on the triplet PES. Moreover, 3HFSiS is found to be the most thermodynamically and kinetically stable and is able to be observed in experiments. Structures2 are the more stable ones between the two group bond cycled isomers and are predicted to be detected. 3SiSHF is the most unstable isomer in thermodynamics and kinetics.