The relativistic Hartree-Fock-Slater (HFSD) approximate method was used in calculating the single-eleotron energy eigenvalues and the energies of Kα, Kβ and Hβ X-rays of rare earth elements Ao, Th, Pa and U. Calculations were also carried out by taking account of the relativistio correction to the exchange potential. Our results are in good agreement with experiments (with an accuracy of 0.3%).