Abstract: Based on zone extensometer and homogenization method, the high temperature creep strain curves of different regions of microalloyed 25Cr35NiNb steel welded joints commonly used in ethylene cracking furnace tubes at 900 ℃ and different stress levels (37–55 MPa) were obtained by digital image correlation (DIC) technique. The creep damage mechanism was explored by microstructure analysis. Parameters were determined with the high temperature creep deformation data obtained by DIC technique and by a global optimization algorithm base on genetic algorithms, the creep constitutive model based on hyperbolic sine function was established, and the creep deformation behavior of different regions of the welded joint under different stress levels was predicted, and was verified by tests. The results show that the minimum creep strain rate in the weld region of the welded joint was smaller than that in the base metal region under the same stress levels, indicating that the weld region had better creep deformation resistance than the base metal region. Comparing with the weld region, the base metal region entered the tertiary creep stage earlier and experienced greater creep deformation, and the base metal region at 3–5 mm from the fusion line was the weakest area of the whole welded joint. With the decrease of the stress level, the skeletal carbide M₇C₃ phase in the base metal region transformed into blocky and chain-like M₂₃C₆ phase, and the vermiform NbC phase transformed into coarse blocky G phase. Meanwhile, a large number of dispersed M₂₃C₆ secondary carbides were precipitated in the grains, and creep cavities were formed at the interface between the G phases and the matrix, which interconnected to form cracks. After creep testing under different stress levels, the microstructure of the weld region still maintained a skeletal shape, indicating a low degree of creep damage. The creep strain predicted by the creep constitutive model was in good agreement with test results, and the average relative error was less than 5%, indicating that the model could effectively predict the non-uniform creep deformation behavior of microalloyed 25Cr35NiNb steel welded joint.