Abstract: On the basis of Surface Complexation Model(SCM), a thermodynamic model for the interface of metal oxide/water dispersion (1:1 electrolyte system), which combined the Electrical Double Layer (EDL) model with. thermodynamic equilibrium principles, was set up. Methods for complete evaluation of parameters in the model and calculation of the concentration distribution were proposed and a corresponding versatile computer program was compiled. The empiricism brought about by the adjustable parameters in SCM was averted. The solution of the model is based experimentally only on the relation between electrokinetic potential (zeta potential) and pH value.