Abstract: The shape and thickness of intermetallic layer (IMC) near the titanium alloy have a significant effect on the mechanical properties of titanium/aluminum dissimilar welding-brazing joints. The process of crack initiation and propagation at nanoscale cannot be obtained directly by the traditional method of microstructure characterization and macroscopic mechanical property test. Based on this, the tensile fracture behavior at the interface IMC of the titanium/aluminum fusion brazing joint was studied by in-situ TEM characterization technique to clarify the influence of the interface IMC on the mechanical properties of the joint. The results show that the main phases of IMC are TiAl and TiAl₃. During the in-situ TEM tensile process, dislocation pile-up was easy to occur at the grain boundary in the fusion zone, and the cracks tended to initiate and propagate at this location. The interfacial layer is not the weak zone of the tensile specimen, and the specimen tends to fracture in the fusion welding zone or on the side of the titanium alloy.