The effect of diffusion welding process parameters on the microstructure, mechanical properties and deformation of Ti₂AlNb alloy welded joints was studied. The results show that when the welding temperature, pressure, and holding time are low, the weld line of Ti₂AlNb diffusion welding joint is distinct, and the mechanical properties are inferior. With the increase of welding temperature, pressure, and holding time, the size of the newly formed equiaxed α₂ phase in the welding zone enlarges, the weld line gradually becomes indistinct, and the mechanical properties, the welding deformation rate of the Ti₂AlNb diffusion welded joint increase. Based on the microstructure of the weld interface, welding deformation rate, and mechanical properties, the optimal Ti₂AlNb diffusion welding process parameters are 960 ℃, 5 MPa, and 120 min. Under this condition, the welding deformation rate is 5.4%. The Ti₂AlNb diffusion welded joint consists of B₂ phase matrix, some coarse lath-like α₂ phase, some equiaxed granular α₂ phase and some O phase distributed within the B₂ phase matrix. The tensile strength reaches 891 MPa at room temperature and 464 MPa at 700 ℃.