Nuclear power pipeline ice plug technology, as the main technical method of nuclear power safety maintenance and innovative design, plays a protective role in the long-term safe operation of nuclear power plants. During the ice plug process, pipelines have complex stress states, which can easily lead to problems such as material yielding, cracking, and even damage. In this study, by building an ice plug test platform for nuclear power pipelines, an ice plug test and a numerical analysis of nuclear power pipelines are carried out to explore the stress distribution of nuclear power pipelines during the ice plug process and its impact on the performance of pipeline materials and to analyze the safety of pipelines in the ice plug process. This study shows that the distribution of stress in the pipeline during ice plug is related to the temperature change and cooling rate of the pipe wall. The stress distribution in different parts is uneven, and the maximum stress appears near the edge of the jacket. According to the temperature data of the pipe wall, the stress distribution of the pipe wall can be obtained by the finite element method. From the test and finite element results, it can be seen that when the frost line length of the pipeline is less than 200 mm, the pipeline ice plug method is safe and feasible.