Abstract: To effectively improve the specific strength of aircraft and enhance fuel utilization efficiency, it is necessary to realize reliable joining between GH4099 alloy and Ti₂AlNb alloy. GH4099 alloy exhibits excellent high-temperature strength, oxidation resistance, and corrosion resistance, while Ti₂AlNb alloy offers advantages such as low density and high specific strength. Achieving reliable joints between these two alloys is of great significance for the upgrading of aerospace equipment. Pure Zr, Cu, Ti, and Ni metal foils were adopted to synthesize the brazing filler metal in-situ at 920 ℃ with a holding time of 15 min, realizing the brazed joining of the two alloys. The results indicate that the typical interface of the brazed joint exhibits a multi-layer metallurgical bonding structure. From the Ti₂AlNb side to the GH4099 side, the following phases are sequentially formed: B2 phase, β-(Ti, Nb) solid solution, intermetallic compound phases such as Ti₂Ni(Al, Nb) and (Ti, Zr, Nb)₂(Cu, Ni), and (Ni, Cr)-based solid solution phase. With the increase of Cu content in the filler metal, the microstructure and properties of the joint change gradually. At an excessively low Cu content, the brazed seam presents island-like and dendritic microstructures, and a continuous reaction layer cannot be formed at the interface. When the mass fraction of Cu increases to 15%, the reaction layer of the brazed seam becomes continuous and dense, and the shear strength reaches a maximum value of 175.0 MPa. As the mass fraction of Cu further increases to 26%, the brittleness of the joint increases; the strength decreases; the fracture mode is brittle fracture.