The development of nuclear power is an important part of the national energy security strategy. Nuclear power safety is the most basic requirement for the development of nuclear power. Based on the testing historical data and expert data of nuclear power heat transfer tubes, the integrity of heat transfer tube degradation is evaluated by using the theory of total probability and Bayes formula. By analyzing the influencing factors such as stress corrosion and fatigue damage, the probability calculation of the degradation distribution of the heat transfer tube under different stress corrosion and fatigue damage conditions is realized. The evaluation method can simplify the complex problem of multiple influencing factors into the correction of a single influencing factor one by one, which simplifies the calculation and processing method. This method can be used for evaluating the degradation probability of heat transfer tubes in nuclear power steam generator.