The sessile drop method was used in the present experiment to study the spreading wetting principle. It is found that 700 K is an important point for the spreading mechanism of the alloy. DTA (Differential Thermal Analysis) was used to analyze the interfacial reaction and the Kissinger method was used to calculate the reaction thermo-kinetics parameters. In addition, it was investigated that element Cu improved the activation energy of Sn-Ag-Cu/Cu system, and suppressed interface reaction rate.