For benzonitrile and cyanotoluene isomers, the near-threshold photoionization corresponds to the photoionization of electrons on HOMO and HOMO-1. The molecule orbital shape for the HOMO and HOMO-1 of toluene and benzene are basically consistent, so the photoionization cross-sections of toluene and benzene 20 are very similar. Besides, compared with other aromatic compounds, benzene has the highest symmetry, it show s obvious Rydberg states characteristics. It's interesting to see the key role of the benzene ring during photoionization for the studied aromatics. Nevertheless, if this finding can be extrapolated to other mono-or di-aromatic compounds requires further investigation on the effect of various substitutions.