Abstract: This article is a theoretical study about ionization equilibrium. Taking the ionization equilibrium of acetic acid in a series of MeOH-water mixtures as an example, we calculated the ionization constant Ka according to the IPF theory, the Born theory and the vander Waals theory, respectively. The results indicate that the values obtained by the IPF theory are in best accordance with those from literatures. A brief discussion about the theories is given at the end.

Key words: IPF theory, Ionization constant, Non-water solvent