Zirconium alloys are commonly used for manufacturing nuclear industry parts and have been widely studied by scientists because of their excellent corrosion resistance. Samples with sizes of 5, 10, and 20 mm were welded via tungsten inert gas welding, and ZrTiNb was used as the welding material. The microstructure of the weld zone is a coarse layer bundle and a small amount of basket-weave widmanstätte structure, which is related to the cooling rate. The microstructure of the fusion zone is composed of smaller widmanstätten grains, which have a clear boundary with the heat-affected zone. The microstructure of the heat-affected zone consists of irregularly serrated equiaxed α phase grains. The microstructure of the base material consists of the as-cast α equiaxed grains. As the distance from the weld zone increases, the grain size decreases. Then, the mechanical properties were tested, and the results show that as the thickness of the sample increased, the plastic extension strength and tensile strength first increases and then decreases, especially a significant decrease at a thickness of 20 mm. The elongation and reduction in the area after fracture of the 10 and 20 mm samples are similar but show an increasing trend compared to those of the 5 mm samples. This article characterizes the microstructure and mechanical properties of ZrTiNb, providing necessary data to support its engineering applications.