Effect of different heat treatment processes on the microstructure and mechanical properties of TIG welded Hastelloy X welded joints was studied by SEM and EDS. The results showed that the central area of the weld was mainly composed of fine equiaxed grains, and the fusion zone was dominated by dendrites. The secondary phase was not precipitated in the weld joints heat treated at 1050°C, and a large number of secondary phases were precipitated in the grains at the grain boundary at 1100°C. The secondary phase at 1150°C were partly re-dissolved. The tensile strength of joint reaches up to 773.49 MPa after heat treatment at 1150°C. The joint treated at 1100°C was intergranular fractures, the rest were ductile fractures.