Abstract: The medium temperature of an elevated temperature molten salt pump is the key factor affecting the fatigue of bolts. The temperature change makes the bolts at the flange connection bear the temperature difference load, which produces alternating stress and leads to the fatigue failure of bolts. In this paper, the fatigue strength of molten salt pump bolts under normal temperature, temperature difference, and same temperature conditions is studied by introducing the temperature difference load into the bolt force analysis. The results show that: in any working condition, when the temperature difference between the bolt and the flange of the molten salt pump is greater than 20 ℃, the number of cycles will be less than 10~4 Under the same temperature condition, when the temperature is greater than 75 ℃, the number of cycles is less than 10~4, entering the low cycle fatigue category. The influence of temperature difference on bolt fatigue when the bolt temperature of the molten salt pump is constant and the flange temperature is rising greater than that when the flange temperature is constant and the bolt temperature is rising. However, although the number of cycles of the latter condition will increase, the sealing will become worse, resulting in the occurrence of leakage. Compared with the temperature difference, the same temperature is the best working condition. The temperature difference caused by the frequent fluctuation of molten salt temperature should be avoided as far as possible.