Abstract: A study on the microstructure, mechanical properties, and heat treatment process of pure tantalum TIG joints was conducted. Industrial computed tomography (CT), OM, and SEM were used to characterize the microstructure of the joints, and a microhardness tester and a universal testing machine were utilized to test the microhardness, tensile properties, and bending properties of the joints. The results indicate that welding parameters play a decisive role in weld formation. An excessively small welding current leads to incomplete penetration, while an excessively large welding current causes burn-through. An excessively high welding speed results in incomplete penetration and undercutting, whereas an excessively low welding speed increases the width of the heat-affected zone. A welding current of 280–320 A and a welding speed of 150–180 mm/min are optimized as the process window. Under these parameters, the maximum tensile strength of the joints reaches 262 MPa, and the fracture surface exhibits dimple characteristics. All fractures initiate in the heat-affected zone and propagate along the softened region near the fusion zone. Based on the optimized parameters, the effect of heat treatment temperature is studied. It is found that as the annealing temperature increases, the residual stress of the weld significantly decreases from 142.17 MPa to 10.69 MPa at an annealing temperature of 1 320 °C, and the tensile strength decreases to 194 MPa due to grain coarsening. By considering the comprehensive effects of stress relief and property loss, 1 320 °C is determined as the optimal annealing temperature. Actual structures are welded using the optimized process. Verified by non-destructive testing and metallographic examination, there are no internal defects in the joints, demonstrating good quality.