The Ag-Cu-Te ternary system is of thermoelectric application interests. The phase diagrams of Ag-Cu-Te ternary system and the Ag2Te/Cu interfacial reactions at 400 ℃ and 600℃ are investigated in this study. Ternary alloys of Ag-Cu-Te were prepared and equilibrated at 400℃ and 600℃, and their equilibrium phases are determined. The phase diagrams of the binary systems, Ag-Te and Cu-Te, were reassessed. In the Ag-Te binary system, there are two compounds, Ag2Te, Ag1.9Te and Ag5Te3. There are three binary compounds, Cu2Te, Cu3Te2 and CuTe, in the binary Cu-Te system. There is one ternary compound, AgCuTe. Isothermal sections at these two temperatures were constructed based on the ternary experimental results, the phase diagrams of the three constituent binary systems, and experimental results of the ternary system in the literature. Two reaction phases, Ag and AgCuTe, are found in the reaction couples. The reaction path is illustrated using the determined isothermal section.