Abstract: The geometry, thermodynamic selectivity and UV-vis spectra of Pu(NO₃)₄TBP₂ and Pu(NO₃)₂DBP₂ in the gas phase were investigated by using B3LYP density functional theory method with the RECP basis for Pu and 6-311 g(d,p) basis for other atoms. The structure optimization results show the bond length between Pu and DBP is shorter than the length between Pu and TBP for the steric hinder of the ligands, and NPA charge analysis shows more electron trasnfer between DBP and Pu ion indicating the stronger coordination ability of DBP. The free energy of ligand exchange between Pu(NO₃)₄TBP₂ and HDBP was -178.9 kJ/mol, indicating the higher coordination affinity between DBP and Pu. The UV-vis absorption spectra of Pu(NO₃)₄TBP₂ in the gas phase were pmainly from nitrate to f orbital of Pu, TBP ligand made few contribution, yet the absorption spectrum of Pu(NO₃)₂DBP₂ were both from nitrate to f orbital of Pu and the ligand-to-metal charge transfer between DBP and Pu.