CVD diamond thick film was brazed to cemmented carbide using a Ag-Cu-Ti active filler metal. The brazing process was performed in a vacuum furnace under different processing condition. The interfacial microstructure and characterization between diamond and Ag-Cu-Ti filler metal were studied by SEM, EPMA and EDX. The morphology and distribution of new compound are shown for the first time (Figs). Results illustrate that a small amount of new compound TiC, TiCu compound exist in the interface. TiC layer exists in the interface and it's thickness is variational with the varying of processing condition such as peak heating temperature, keeping time and so on. New compound TiC accretes with the surface atoms of diamond in a special section, and particular orientation relationships are occasionally observed by examining the fracture section. TiCu layer near TiC exists in the interface. It is worth notice that too much TiC and TiCu in interface could weaken join strength because TiC and TiCu are brittle.