Abstract: In this paper, numerical simulation study is conducted for the flow of coolant in the top nozzle of the fuel assembly based on CFD methodology and the general simulation settings have been proposed. Comparison between the results of measured coefficient in the experiment and CFD simulation validated the feasibility of this calculation method. Based on CFD simulation, the resistant characteristics of different components of the top nozzle had been evaluated. The analysis and evaluation showed thatt the main reason for the difference of the experiment data of the top nozzle with the reference data is the resistance coefficient value of the fuel assembly top nozzle. Recommended value is proposed.