DFT/BLYP method is used to investigate theoretically the electron transfer (ET) reactions between M(Li, Na, Mg)-C6H6 and M+-C6H6 complexes in the gas phase. The geometry optimization of the metal-benzene complexes and the encounter state in the process of ET reaction was performed at 6-31G basis set level. The precursor complex has C6 symmetry, the distance between acceptor and donor is about 0.30～0.36 nm, which yields the bonding energy approximately 0.9～1.5 eV. It shows that there are relatively strong interactions between them. The geometry of transition state is also obtained by the linear coordinate method. The activation energy, the coupling matrix element and the rate constant of the ET reaction are calculated. According to the reorganization energy of the ET reaction, the values obtained from George-Griffith-Marcus (GGM) method (the contribution only comes from the dia nal elements of the force constant matrix) are larger than those obtained from Hessian matrix method (including the contribution from both dia nal and off -dia nal elements),which suggests that the coupling interactions between different vibrational modes are important to the inner-sphere reorganization energy for the ET reactions in gaseous phase.