Abstract: To investigate the high-temperature burst performance and microstructural evolution of the Zr-4 end plug and CZ cladding tube under different welding parameters, specimens were fabricated using self-developed pressure resistance welding equipment, and their microstructures and properties were characterized. The results indicate that high-quality interfacial bonding without oxide layer formation is achieved under different welding parameters. The electrochemical characterization results confirm that the welding thermal cycle has no significant effect on the microstructure and chemical composition of the heat-affected zone, demonstrating that the process has good compatibility with the intrinsic stability of the materials. The high-temperature burst test at 360 °C shows that the specimens all fracture in the base metal region of the cladding tube, verifying that the strength of the welded joint is higher than that of the base metal. Microstructural analysis indicates that the grain size of the joint is affected by the upset length, and its evolution is synergistically determined by the thermal input and plastic deformation. The disparity in grain size between the end plug side and the tube side originates from the comprehensive effects of the thermal conductivity gradient, plastic deformation capacity, and grain boundary pinning effect of the second phase. The weld zone is predominantly composed of lath-shaped α-Zr accompanied by trace β-Zr precipitates, while the low-heat-input region presents an equiaxed α-Zr morphology. The second phase distribution exhibits significant spatial heterogeneity: The end plug side only contains a trace amount of Zr(Fe,Cr)₂-type Laves phase, whereas the tube side is enriched with nano-sized β-Nb precipitates and localized Zr(Fe,Cr)₂ phase and Zr(Nb,Fe)₂ phase.