Abstract: The dropping time and profile of control rods are important parameters during the safety evaluation of nuclear power plants. CFD method and dynamic mesh were used to study the dropping profile of the control rod and flow evolution.  The changes of displacement, velocity and acceleration versus time during the dropping of the control rod are obtained. Meanwhile, the effect of the deformation of the control rod and channel on the control rod dropping is evaluated. The results of the work are of help to the design and optimization of the structure of control rods.