Abstract: A smart nuclear reactor control rod drive line was used as the research object,and a 3-D fluid simulation model of single control rod dropping was set up.Velocity and pressure nephogram in the guide tube were obtained by simulating the control rod dropping behavior based on dynamic grid technique,and the displacement cure,velocity cure and pressure cure were obtained as well.Comparison of the simulation and experiment results showed that the simulation results were in good agreement with the experimental results.Some important parameters can be calculated by this method,such as the time of control rod dropping process and the maximum impact force,so it can provide references for the design of control rod drive line structure.