Electronic structure of atom cluster Fe4B, taken as a tetrahedron, is calcu lated by using the self-consistent field Xα-scattered-wave method. The energy levels, contour maps and densities of states for the atom clusters Fe4 and Fe4B are analyzed and compared respectively, the effect of the B atoms on the electronic structure of atom cluster Fe4B is discussed, and some physical nature of amorphous alloy Fe80B20 is also discussed.