Density functional calculations were performed on a series of mixed-ligand organolanthanide complexes, (η 5 -C 5 H 5 ) 2 LnX.OC 4 H 8 (η 5 -C 5 H 5 =Cp; Ln=La-Lu; X=F, Cl, Br and I; OC 4 H 8 =THF). The calculated geometrical parameters are in reasonable agreement with the experimental data. The distances between Ln and ligands follow linearity along the ionic radius of lanthanide metal, as the same as that observed in experiment. In the mixed-ligand complexes, Ln-Cp and Ln-THF bonds are more covalent compared to Ln-X. The lanthanide contraction of various bond and the metal-ligand interaction energy followed the order of Ln-X>Ln-Cp>Ln-OC 4 H 8 . The orbital population and dipole moment were also discussed.