Abstract: A new method for predicting the surface tension of ternary from biliary ones by using geometric solution model is given. Binary excess surface tensions are fitted by means of rational function method, and ternary excess surface tension are calculated using R-function method. That makes not only the calculaiton time to be less, but the results to be more accurate. This method was appliced to the Cu-Ag-Au system, and a good accordance was obtained between the calculated and reference values.