The ab initio coupled-cluster theory and the configuration interaction method have been used to optimize the possible ground state structures of NH, NO and HNO. The potential energy functions of HNO have been derived from the many-body expansion theory. In the symmetric stretching vibration and rotation potential energy diagram of HNO, there are saddle points in reaction kinetics O+NH→HNO, H+NO→HNO, N+HO→HNO, when O, H, N atoms with the energies surpassing 1.153 eV, 1.683 eV, 2.216 eV respectively, a stable HNO molecule could be formed. These are reported for the first time so for as we know. In addition, It is reported that the position of HNO’s isomer in the curve and the energy of transition from HNO to HON are also determined.