Abstract: To implement the process of rod cluster control assemblies（RCCA） dropping in PWRs, the dashpot structure below the guide thimble is designed. The select of the dashpot structure parameters has a great influence on the effect of the RCCA damping. In this paper, the theory model about the RCCA damping in the control rod dropping process is established, and the sensitivity analysis is carried out by changing the dashpot structure parameters, including the diameter and the length of the screw hole, and the gap between the rod and the guide thimble. The parameter influence regularity has been deduced to guide the guide thimble component design in the primary process in future.