Theoretical studies on metal bis(trifluoromethylsulfonyl)imides, M(TFSI)(2) (M = Mg, Ca, Ba, Zn, and Cu) are carried out using density functional theory (DFT) method and B3LYP/lanl2dz theory level for the first time. Quadradentate structures involving four oxygen atoms of four -SO2- groups are preferred. Based on these conformations, binding energies and frontier molecular orbital (FMO) energies have been compared, correlated with experimental results, to evaluate the Lewis acidity and catalytic activity of these metal complexes. Wave function analyses have been performed by natural bond orbital (NBO) method to further investigate the cation-anion interactions. M(TFSI)(2)-acrolein complexes are also calculated at the same level to obtain a better understanding of the interactions between Lewis acid and dienophile. Several important trends are revealed and give an insight into the molecular structures and Lewis acidity of M(TFSI)(2), as well as the weakly coordinating property of TFSI- anion. Explanations for the outstanding catalytic property of Cu(TFSI)(2) are put forward. Predictions upon a novel Lewis acid are also provided.