Potential energy surface of HNOS system is investigated by means ofMP2 method with 6-311 ++ G(d, p)basis set. The energyfor each minimum and saddle point on the potential energy surface is corrected at the QCISD(T)/6-311 ++ G(3df, 2p) level of theory with zero-point vibrational energy included. As a result, eighteen isoners are theoretically predicted and cis-HNSO is found to be global minimum on the potential energy surface. Wherein, fourteen isoners are considered as kinetically stable species, and should be experimentally observed. Comparisons are made for HNOS system with its analogues, HNO2 and HNS2. The nature of bonding and isomers' stability of HNOS system are similar to HNS2. The obvious similarities and discrepancies among HNOS, HNO2 and HNS2are attributed to the hypervalent capacity of sulfur, oxygen and nitrogen atoms.