The interaction of cation/benzene complexes (cation = Na+, Li+, K+) was calculated by using the density functional theory (DFT). The calculated results suggested that the C-H bonds were strengthened and the C-C bonds were weakened in cation/benzene complexes in comparison to that in free benzene. This conclusion was confirmed by the changes in the stretching frequencies. The redistribution of the charges and the rehybridization analysis of the C-H and C-C bonds gave a further understanding. Similar phenomena have also been found in cation/perfluorobenzene, cation/naphthalene, cation/toluene,. and cation/aniline systems.