Abstract: In order to ensure the safety of the accelerator driven subcritical system (ADS), the numerical simulation for thermal stratification of ADS LBE natural circulation was presented by using computational fluid dynamics (CFD) method. The results show that in LBE natural circulation, the most serious area of thermal stratification exists in heating zone and the hierarchical state of thermal stratification in the loop is different. When the temperature difference in the loop is bigger, the flow velocity increases, and the thermal stratification is more obvious. When the diameter of the loop pipe is larger, the flow velocity becomes lower, and the thermal stratification is not obvious. When the velocity is lower, thermal stratification of local area tends to disappear. When the velocity is bigger, the temperature difference increases in the cross section with maximum temperature difference.