Abstract: Quantum chemistry method is used to study the constituted mass spectrum of the propanol.The relative ions and fragments in the mass spectrum of the propanol are re examined.Molecular orbital and ZPE calculations conducted at the MP2/6 31G  //UHF/6 31G  level were used to characterize the corresponding potential energy profile.The unimolecular reactions of the molecular ion and the fragments of propanol are investigated,that involiving dehydrogenation,rearrangement,isomerization and fragmentation.The results of ab initio show the configurations of the fragment ions and the ion neutral complexes,and explain why the molecular ion is very weakly in the mass spectrum.It is explained that some of the theoretical species of ion neutral complexes are unavailable in effect at the mass spectrometry to account for the energies.The ion C 3H 7O + comprises multi isomer consisting of ethene and protoned formaldehyde ion.The isomerization of C 3H 7O + ion is essentially the reorientation of the two partners CH 2OH + and C 2H 4.