In order to reveal the behaviors of Fe and RE atoms on grain boundaries in ZA27 alloy theoretically, the atomic structure model of high angle grain boundary of α phase in ZA27 alloy was set up by using the concept of coincidence-site lattice(CSL). The electronic structure (state density, Fermi energy level, structure energy) of grain boundary was calculated using the recursion method. The clustering energy of alloying atoms was defined by the structure energy of grain boundary, and the clustering energies of Fe or RE atoms on grain boundary was calculated. The calculated results show that: the clustering energy of Fe or RE atoms gathered on grain boundary in ZA27 alloys is positive, so they can not form clusters and have the ordering tendency. Fe and RE atoms prefer to form steady inter_metallic compounds, and can form the negative electricity center on grain boundary in ZA27 alloys, thus reducing the Fermi energy level of grain boundary.