Abstract: Interactions between ions and solvent as well as between ions themselves in a methanol solution of lithium perchlorate were studied by IR spectrometry. As shown by the experimental results, the spectral change of solvent molecule, i.e., the molecule of CH3OH, was due to the interaction between the Li+ ion and CH3OH molecule leading to hypsochromic shift of stretching vibration of O-H group, and it was deduced that the hydrogen bonds between CH3OH molecules were destroyed by the solvation of Li+ ion. Ion association between Li+ and ClO-4 to form (Li+ClO-4) ion pair and its dimer (Li+ClO-4)2 was proved by the change of characteristic bands of ClO-4 ion. Based on the density-functional theory, optimization of structures of the coordination complex ［Li(CH3OH)n］+ with different solvation numbers from 1 to 4 and the ion association complexes of (Li+ClO-4) and (Li+ClO-4)2 as well as the thermodynamic parameters were calculated.