We present here an in-depth study upon the interaction between a neutral cluster Al-13 and a typical ligand tetrahydrofuran (THF) via density functional theory (DFT) calculation. It is found that electron delocalization over the framework of Al-13 and THF facilitates ligand-to-Al-13 charge transfer leading to enhanced stability for the superhalogen cluster Al-13. Further study on the stabilization of Al-13(THF)(n) cluster complexes with n = 1-8 reveals that the adsorption of more THF ligands gradually enhances the total binding energy and the total electronic charge transfer from the ligand to Al-13. The bonding nature and stabilization of Al-13(THF)(n) cluster are then demonstrated by rationalizing the interactions between superatomic and molecular orbitals of Al-13 and THF, respectively.