The microstructures and fracture morphologies at the weld interfaces of near isothermally forged and heat treated Ti3Al/TC11 dual alloy after thermal exposure at 550 °C for 50 h were investigated through tensile experiment and using OM and SEM. The results indicate that under gradient heat treatment the tensile strength of dual alloy after thermal exposure increases as the increase of the deformation degree; meanwhile, the interlaced structures of the acicular α phase in weld interface decompose and coarsen, and more fined sphericity α/α2 phases precipitate in weld. The strength of the dual alloy processed by gradient heat treatment is slightly higher than that by double heat treatment after thermal exposure. α2 phase in Ti3Al HAZ of specimen processed by double heat treatment grows up during thermal exposure. Mechanical properties of the specimen without oxidation surface are superior to that with oxidation surface due to the surface microcrack caused by oxidation. It can be found that fracture predominantly occurs in Ti3Al base alloy from the facture position of specimens.