Metallic materials undergo creep during long-term high-temperature service, leading to new failure modes. Structural integrity assessments for high-temperature structures, such as creep and creep-fatigue, are critical issues requiring focused attention. The analysis process for high-temperature creep differs significantly from conventional static or dynamic analyses. Existing strength evaluation criteria for high-temperature components are primarily based on elastic analysis methods outlined in the ASME code, which involve complex procedures, extensive calculations, and are prone to human errors or deviations. This study investigates high-temperature creep evaluation methods based on the ASME III D.5 design criteria and develops a high-temperature structural integrity assessment software. The software includes time-dependent primary stress limits, total cumulative inelastic strain limits, and creep-fatigue damage assessments for base metals and welded structures in high-temperature zones of nuclear power plants operating above creep temperatures. This tool provides an efficient and accurate solution for conducting high-temperature structural integrity evaluations in the design of fourth-generation high-temperature nuclear power plants.