Abstract: The dynamic characteristics of the thrust bearing for one nuclear power plant reactor coolant pump（RCP） during loss of power coastdown has been simulated and analyzed. Firstly the axial force of the RCP rotor has been derived. Then a mathematical model for the thrust bearing has been established based on Reynolds lubrication theory, afterwards the model is numerically solved by finite difference method and a calculation code is programed. The code is then validated through the calculation and comparison with some design operation conditions of the RCP thrust bearing. The dynamic characteristics of the thrust bearing during loss of power coastdown under hot and cold condition is simulated and calculated separately, and the calculation results suggest that when the RCP being coastdown to low speed under hot condition, the minimum oil film thickness of the thrust bearing will be less than the empirically safe margin and the maximum temperature increases sharply, which is adverse to the safe operation of the RCP. Meanwhile coastdown in cold condition is predicted to be safe.