Abstract: A Ag-Cu-Ti alloy is one of the most extensive brazing alloy for joining of ceramics to metals with active metal brazing method.The activity of Ti as a alloy element is a key factor influencing the interface reaction between ceramics and the brazing alloy,and plays an important role in wettability and joining ability of ceramics by the brazing alloy.In this paper,the Ag-Cu-Ti brazing alloy has been analyzed thermodynamically,the Ti activity and its relation to the concentration of the alloy components have been studied,and the interaction parameters of the alloy components have calculated.Results of the analysis and calculation have shown that the activity of Ti decreases with increasing Cu and decreasing Ag content.There is a certain repulsive interaction,32.83 kJ/mol of calculated value,between Ag and Ti,while a strong attractive interaction,-16.14 kJ/mol,between Cu and Ti.In order to improving the activity of Ti,it is helpful to adding some alloy elements to the Ag-Cu-Ti alloy,which has a strong bond with Cu,a weak bond with Ti,and no formation of the high melting point compounds or brittle phases with alloy components.