In order to investigate the influence of notched structures on creep performance under long-term high-temperature conditions, durability tests were conducted on ring-notched and hole-containing thin tubular specimens of directional columnar-grain DZ411 alloy at 850 °C and 930 °C. The results were compared with those of smooth round rod specimens at same temperatures and stress levels, to evaluate the impact of notched structures described above on the rupture life. Based on the experimental data, a finite element subroutine was developed using a macroscopic phenomenological creep model to simulate the creep deformation behavior of the structural components. The stress relaxation characteristics of the two types of notched structures were analyzed. The results show that the ring-notched structure exhibits significant stress relaxation, leading to a “notch strengthening” effect, which improves the endurance property; conversely, the small-hole structure shows insufficient stress relaxation, resulting in “notch weakening” and a reduction in the endurance property. The developed subroutine demonstrates sufficient engineering accuracy in notch creep simulation. Using creep strain as the fracture criterion, the predicted endurance life showed a deviation from experimental results within the acceptable engineering range, indicating that the subroutine has sufficient engineering accuracy.