XPS and NEXAFS spectra of four stable C-40 isomers [29(C-2), 31 (C-s), 38(D-2), and 39(D-sd)] have been investigated theoretically. We combined density functional theory and the full core hole potential method to simulate C 1s XPS and NEXAFS spectra for nonequivalent carbon atoms of four stable C-40 fullerene isomers. The NEXAFS showed obvious dependence on the four C-40 isomers, and XPS spectra are distinct for all four isomers, which can be employed to identify the four stable structures of C-40. Furthermore, the individual components of the spectra according to different categories have been investigated, and the relationship between the spectra and the local structures of C atoms was also explored.