The electronic structure and aromatic characteristic of an unusual C 18 precursor, C 18 Br 6 , were theoretically studied from the perspective of graphical analysis. The skeleton structure of the C 18 Br 6 with alternating long and short C-C bonds, similar to that of C 18 and C 18 (CO) n (n = 2, 4, and 6), is determined by molecular geometry optimization and BO analyses. Like C 18 and C 18 (CO) n (n = 2, 4, and 6), C 18 Br 6 also has three sets of orbital systems composed of different types of electrons. IRI analysis shows that the three MOs are distributed in different ways on the long and short C-C bonds. The π in -orbital is destroyed near the -Br substituents on the cyclocarbon skeleton but the π out -system remains intact, which directly leads to the fact that the π in -electrons in the C 18 Br 6 are only localized in a few regions while the π out -system is globally delocalized. This inference is further confirmed by the analyses of real space functions LOL and ELF. ELF bifurcation values and AV1245 indices for π in -and π out -electron systems quantified the degree of their delocalization in C 18 Br 6 . The clockwise ring current and the shielding/deshielding effect inside/outside the ring induced by external magnetic field rendered from AICD, ICSS, and GIMIC analyses clearly indicate that the C 18 Br 6 is an aromatic species. The destruction of the π in -conjugation caused by the presence of -Br substituents weakens the overall aromaticity of the cyclocarbon skeleton, resulting in the molecular aromaticity of C 18 Br 6 is weaker than that of the C 18 and comparable to that of the C 18 (CO) 6 . This conclusion is supported by NICS quantitative analysis. The relevant results of this work are helpful to further understand the aromaticity of carbon-rich cyclic molecules and provide novel insights into the influence of introducing substituent groups on electron delocalization.