Potential energy surface of HNS 2 is investigated by means of second order Moller Plesset perturbation theory (MP2) and QCISD(T) (single point) methods. At final QCISD (T)/6 311++G(3df,2p)//MP2/6 311++G(d,p) level with zero point vibrational energies included, cis HNSS is found to be global minimum on the potential energy surface, followed by low lying trans HNSS, HN(S)S( C 2v ), cis HSNS, cis HSSN, trans HSNS, trans HSSN, and HN(S)S( C s ) by 13 46, 66 92, 78 25, 80 38, 81 22, 81 38 and 86 40 kJ/mol, respectively. A new high lying HS(N)S isomer with C s symmetry is located on the potential energy surface. The kinetic stabilities of all isomers are predicted. Comparisons are made for HNS 2 with its analogues, HNO 2, HPS 2 and HPO 2. The causes that lead to the differences between HNS 2 and its analogues are hypervalent capacity of phosphorus and distinct electronegativities of hydrogen, nitrogen and phosphorus. At last QCISD (T) / 6 311 ++ G (3df, 2p) // MP2 / 6 311 ++ G (d, p) level with zero point vibrational energies included, cis HNSS is found to be global minimum on the potential energy surface, followed by low lying trans HNSS, HN (S) S , cis HSNS, cis HSSN, trans HSNS, trans HSSN, and HN (S) S (Cs) by 13 46, 66 92, 78 25, 80 38, 81 22, 81 38 and 86 40 kJ / mol, respectively. A new high lying HS (N) S isomer with C s symmetry is located on the potential energy surface. The kinetic stabilities of all isomers are predicted. Comparisons are made for HNS 2 with its analogues, HNO 2, HPS 2 and HPO 2. The causes that lead to the differences between HNS 2 and its analogues are hypervalent capacity of phosphorus and distinct electronegativities of hydrogen, nitrogen and phosphorus .