The effect of Re segregation on the α-Fe∑5 [001](010) grain boundary (GB) is investigated by using a software called Dmol and discrete variational method (DVM). Based on the Rice-Wang model, the calculated segregation energy and defect formation energy show that Re is a strong cohesive enhancer. We also calculated the interatomic energy (IE) and bond order (BO) of several atomic pairs to investigate the mechanism of the cohesive effect of Re microscopically and locally. The results show that Ies of atomic pairs formed by those atoms which cross the plane of GB are strengthened due to the segregation of Re, while the Bos of the corresponding pairs are slightly decreased. This discrepancy demonstrates that IE which contains the Hamiltonian of interaction between atoms is a good quantity to describe the bonding strength. The analysis suggests that the electronic effect between atomic pair which comes directly from Hamiltonian is the key factor. The charge density is also presented, and the result indicates that the bonding strength between the Fe atoms on the GB is enhanced due to the segregation of Re, which is consistent with the analysis of IE.